C# - Environment
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Integrated Development Environment (IDE) For C#
Microsoft provides the following development tools for C# programming:
- Visual Studio 2010 (VS)
- Visual C# 2010 Express (VCE)
- Visual Web Developer
The last two are freely available from Microsoft official website. Using these tools, you can write all kinds of C# programs from simple command-line applications to more complex applications. You can also write C# source code files using a basic text editor, like Notepad, and compile the code into assemblies using the command-line compiler, which is again a part of the .NET Framework.
Visual C# Express and Visual Web Developer Express edition are trimmed down versions of Visual Studio and has the same look and feel. They retain most features of Visual Studio. In this tutorial, we have used Visual C# 2010 Express.
You can download it from Microsoft Visual Studio. It gets automatically installed in your machine. Please note that you need an active internet connection for installing the express edition.
Writing C# Programs on Linux or Mac OS
Although the.NET Framework runs on the Windows operating system, there are some alternative versions that work on other operating systems. Mono is an open-source version of the .NET Framework, which includes a C# compiler and runs on several operating systems, including various flavors of Linux and Mac OS. Kindly check Go Mono.
The stated purpose of Mono is not only to be able to run Microsoft .NET applications cross-platform, but also to bring better development tools to Linux developers. Mono can be run on many operating systems including Android, BSD, iOS, Linux, OS X, Windows, Solaris and UNIX.
C# - Program Structure
C# Hello World Example
A C# program basically consists of the following parts:
- Namespace declaration
- A class
- Class methods
- Class attributes
- A Main method
- Statements & Expressions
- Comments
Let us look at a simple code that would print the words "Hello World":
using System; namespace HelloWorldApplication { class HelloWorld { static void Main(string[] args) { /* my first program in C# */ Console.WriteLine("Hello World"); Console.ReadKey(); } } }
When the above code is compiled and executed, it produces the following result:
Hello World
Let us look at various parts of the above program:
- The first line of the program using System; - the using keyword is used to include the Systemnamespace in the program. A program generally has multiple using statements.
- The next line has the namespace declaration. A namespace is a collection of classes. TheHelloWorldApplication namespace contains the class HelloWorld.
- The next line has a class declaration, the class HelloWorld contains the data and method definitions that your program uses. Classes generally would contain more than one method. Methods define the behavior of the class. However, the HelloWorld class has only one methodMain.
- The next line defines the Main method, which is the entry point for all C# programs. The Mainmethod states what the class will do when executed
- The next line /*...*/ will be ignored by the compiler and it has been put to add additionalcomments in the program.
- The Main method specifies its behavior with the statement Console.WriteLine("Hello World");WriteLine is a method of the Console class defined in the System namespace. This statement causes the message "Hello, World!" to be displayed on the screen.
- The last line Console.ReadKey(); is for the VS.NET Users. This makes the program wait for a key press and it prevents the screen from running and closing quickly when the program is launched from Visual Studio .NET.
Its worth to note the following points:
- C# is case sensitive.
- All statements and expression must end with a semicolon (;).
- The program execution starts at the Main method.
- Unlike Java, file name could be different from the class name.
Compile & Execute a C# Program:
If you are using Visual Studio.Net for compiling and executing C# programs, take the following steps:
- Start Visual Studio.
- On the menu bar, choose File, New, Project.
- Choose Visual C# from templates, and then choose Windows.
- Choose Console Application.
- Specify a name for your project, and then choose the OK button.
- The new project appears in Solution Explorer.
- Write code in the Code Editor.
- Click the Run button or the F5 key to run the project. A Command Prompt window appears that contains the line Hello World.
You can compile a C# program by using the command-line instead of the Visual Studio IDE:
- Open a text editor and add the above-mentioned code.
- Save the file as helloworld.cs
- Open the command prompt tool and go to the directory where you saved the file.
- Type csc helloworld.cs and press enter to compile your code.
- If there are no errors in your code, the command prompt will take you to the next line and would generate helloworld.exe executable file.
- Next, type helloworld to execute your program.
- You will be able to see "Hello World" printed on the screen.
C# - Basic Syntax
C# is an object-oriented programming language. In Object-Oriented Programming methodology, a program consists of various objects that interact with each other by means of actions. The actions that an object may take are called methods. Objects of the same kind are said to have the same type or, more often, are said to be in the same class.
For example, let us consider a Rectangle object. It has attributes like length and width. Depending upon the design, it may need ways for accepting the values of these attributes, calculating area and display details.
Let us look at an implementation of a Rectangle class and discuss C# basic syntax, on the basis of our observations in it:
using System; namespace RectangleApplication { class Rectangle { // member variables double length; double width; public void Acceptdetails() { length = 4.5; width = 3.5; } public double GetArea() { return length * width; } public void Display() { Console.WriteLine("Length: {0}", length); Console.WriteLine("Width: {0}", width); Console.WriteLine("Area: {0}", GetArea()); } } class ExecuteRectangle { static void Main(string[] args) { Rectangle r = new Rectangle(); r.Acceptdetails(); r.Display(); Console.ReadLine(); } } }
When the above code is compiled and executed, it produces the following result:
Length: 4.5 Width: 3.5 Area: 15.75
The using Keyword
The first statement in any C# program is
using System;
The using keyword is used for including the namespaces in the program. A program can include multiple using statements.
The class Keyword
The class keyword is used for declaring a class.
Comments in C#
Comments are used for explaining code. Compilers ignore the comment entries. The multiline comments in C# programs start with /* and terminates with the characters */ as shown below:
/* This program demonstrates
The basic syntax of C# programming
Language */
Single-line comments are indicated by the '//' symbol. For example,
}//end class Rectangle
Member Variables
Variables are attributes or data members of a class, used for storing data. In the preceding program, the Rectangle class has two member variables named length and width.
Member Functions
Functions are set of statements that perform a specific task. The member functions of a class are declared within the class. Our sample class Rectangle contains three member functions:AcceptDetails, GetArea and Display.
Instantiating a Class
In the preceding program, the class ExecuteRectangle is used as a class, which contains the Main()method and instantiates the Rectangle class.
Identifiers
An identifier is a name used to identify a class, variable, function, or any other user-defined item. The basic rules for naming classes in C# are as follows:
- A name must begin with a letter that could be followed by a sequence of letters, digits (0 - 9) or underscore. The first character in an identifier cannot be a digit.
- It must not contain any embedded space or symbol like ? - +! @ # % ^ & * ( ) [ ] { } . ; : " ' / and \. However, an underscore ( _ ) can be used.
- It should not be a C# keyword.
C# - Data Types
In C#, variables are categorized into the following types:
- Value types
- Reference types
- Pointer types
Value Types
The following table lists the available value types in C# 2010:
| Type | Represents | Range | Default Value |
|---|---|---|---|
| bool | Boolean value | True or False | False |
| byte | 8-bit unsigned integer | 0 to 255 | 0 |
| char | 16-bit Unicode character | U +0000 to U +ffff | '\0' |
| decimal | 128-bit precise decimal values with 28-29 significant digits | (-7.9 x 1028 to 7.9 x 1028) / 100 to 28 | 0.0M |
| double | 64-bit double-precision floating point type | (+/-)5.0 x 10-324 to (+/-)1.7 x 10308 | 0.0D |
| float | 32-bit single-precision floating point type | -3.4 x 1038 to + 3.4 x 1038 | 0.0F |
| int | 32-bit signed integer type | -2,147,483,648 to 2,147,483,647 | 0 |
| long | 64-bit signed integer type | -923,372,036,854,775,808 to 9,223,372,036,854,775,807 | 0L |
| sbyte | 8-bit signed integer type | -128 to 127 | 0 |
| short | 16-bit signed integer type | -32,768 to 32,767 | 0 |
| uint | 32-bit signed integer type | 0 to 4,294,967,295 | 0 |
| ulong | 64-bit signed integer type | 0 to 18,446,744,073,709,551,615 | 0 |
| ushort | 16-bit signed integer type | 0 to 65,535 | 0 |
Reference Types
The reference types do not contain the actual data stored in a variable, but they contain a reference to the variables.
In other words, they refer to a memory location. Using more than one variable, the reference types can refer to a memory location. If the data in the memory location is changed by one of the variables, the other variable automatically reflects this change in value. Example of built-in reference types are:object, dynamic and string.
OBJECT TYPE
The Object Type is the ultimate base class for all data types in C# Common Type System (CTS). Object is an alias for System.Object class. So object types can be assigned values of any other types, value types, reference types, predefined or user-defined types. However, before assigning values, it needs type conversion.
When a value type is converted to object type, it is called boxing and on the other hand, when an object type is converted to a value type, it is called unboxing.
object obj; obj = 100; // this is boxing
DYNAMIC TYPE
You can store any type of value in the dynamic data type variable. Type checking for these types of variables takes place at runtime.
Syntax for declaring a dynamic type is:
dynamic <variable_name> = value;
For example,
dynamic d = 20;
Dynamic types are similar to object types except that type checking for object type variables takes place at compile time, whereas that for the dynamic type variables takes place at run time.
STRING TYPE
The String Type allows you to assign any string values to a variable. The string type is an alias for the System.String class. It is derived from object type. The value for a string type can be assigned using string literals in two forms: quoted and @quoted.
For example,
String str = "Tutorials Point";
A @quoted string literal looks like:
@"Tutorials Point";
The user-defined reference types are: class, interface, or delegate. We will discuss these types in later chapter.
Pointer Types
Pointer type variables store the memory address of another type. Pointers in C# have the same capabilities as in C or C++.
Syntax for declaring a pointer type is:
type* identifier;
For example,
char* cptr; int* iptr;
C# - Type Conversion
Type conversion is basically type casting, or converting one type of data to another type. In C#, type casting has two forms:
- Implicit type conversion - these conversions are performed by C# in a type-safe manner. Examples are conversions from smaller to larger integral types and conversions from derived classes to base classes.
- Explicit type conversion - these conversions are done explicitly by users using the pre-defined functions. Explicit conversions require a cast operator.
C# Type Conversion Methods
C# provides the following built-in type conversion methods:
| S.N | Methods & Description |
|---|---|
| 1 | ToBoolean Converts a type to a Boolean value, where possible. |
| 2 | ToByte Converts a type to a byte. |
| 3 | ToChar Converts a type to a single Unicode character, where possible. |
| 4 | ToDateTime Converts a type (integer or string type) to date-time structures. |
| 5 | ToDecimal Converts a floating point or integer type to a decimal type. |
| 6 | ToDouble Converts a type to a double type. |
| 7 | ToInt16 Converts a type to a 16-bit integer. |
| 8 | ToInt32 Converts a type to a 32-bit integer. |
| 9 | ToInt64 Converts a type to a 64-bit integer. |
| 10 | ToSbyte Converts a type to a signed byte type. |
| 11 | ToSingle Converts a type to a small floating point number. |
| 12 | ToString Converts a type to a string. |
| 13 | ToType Converts a type to a specified type. |
| 14 | ToUInt16 Converts a type to an unsigned int type. |
| 15 | ToUInt32 Converts a type to an unsigned long type. |
| 16 | ToUInt64 Converts a type to an unsigned big integer. |
The following example converts various value types to string type:
namespace TypeConversionApplication { class StringConversion { static void Main(string[] args) { int i = 75; float f = 53.005f; double d = 2345.7652; bool b = true; Console.WriteLine(i.ToString()); Console.WriteLine(f.ToString()); Console.WriteLine(d.ToString()); Console.WriteLine(b.ToString()); Console.ReadKey(); } } }
When the above code is compiled and executed, it produces the following result:
75 53.005 2345.7652 True
C# - Variables
A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C# has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.
We have already discussed various data types. The basic value types provided in C# can be categorized as:
| Type | Example |
|---|---|
| Integral types | sbyte, byte, short, ushort, int, uint, long, ulong and char |
| Floating point types | float and double |
| Decimal types | decimal |
| Boolean types | true or false values, as assigned |
| Nullable types | Nullable data types |
C# also allows defining other value types of variable like enum and reference types of variables likeclass, which we will cover in subsequent chapters. For this chapter, let us study only basic variable types.
Variable Definition in C#
Syntax for variable definition in C# is:
<data_type> <variable_list>;
Here, data_type must be a valid C# data type including char, int, float, double, or any user-defined data type, etc., and variable_list may consist of one or more identifier names separated by commas.
Some valid variable definitions are shown here:
int i, j, k; char c, ch; float f, salary; double d;
You can initialize a variable at the time of definition as:
int i = 100;
Variable Initialization in C#
Variables are initialized (assigned a value) with an equal sign followed by a constant expression. The general form of initialization is:
variable_name = value;
Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as:
<data_type> <variable_name> = value;
Some examples are:
int d = 3, f = 5; /* initializing d and f. */ byte z = 22; /* initializes z. */ double pi = 3.14159; /* declares an approximation of pi. */ char x = 'x'; /* the variable x has the value 'x'. */
It is a good programming practice to initialize variables properly, otherwise sometimes program would produce unexpected result.
Try the following example which makes use of various types of variables:
namespace VariableDefinition { class Program { static void Main(string[] args) { short a; int b ; double c; /* actual initialization */ a = 10; b = 20; c = a + b; Console.WriteLine("a = {0}, b = {1}, c = {2}", a, b, c); Console.ReadLine(); } } }
When the above code is compiled and executed, it produces the following result:
a = 10, b = 20, c = 30
Accepting Values from User
The Console class in the System namespace provides a function ReadLine() for accepting input from the user and store it into a variable.
For example,
int num; num = Convert.ToInt32(Console.ReadLine());The function Convert.ToInt32() converts the data entered by the user to int data type, becauseConsole.ReadLine() accepts the data in string format.
Lvalues and Rvalues in C#:
There are two kinds of expressions in C#:
- lvalue: An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment.
- rvalue: An expression that is an rvalue may appear on the right- but not left-hand side of an assignment.
Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned and can not appear on the left-hand side. Following is a valid statement:
int g = 20;
But following is not a valid statement and would generate compile-time error:
10 = 20;
C# - Constants and Literals
The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well.
The constants are treated just like regular variables except that their values cannot be modified after their definition.
Integer Literals
An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for
An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order.
Here are some examples of integer literals:
212 /* Legal */ 215u /* Legal */ 0xFeeL /* Legal */ 078 /* Illegal: 8 is not an octal digit */ 032UU /* Illegal: cannot repeat a suffix */
Following are other examples of various types of Integer literals:
85 /* decimal */ 0213 /* octal */ 0x4b /* hexadecimal */ 30 /* int */ 30u /* unsigned int */ 30l /* long */ 30ul /* unsigned long */
Floating-point Literals
A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form.
Here are some examples of floating-point literals:
3.14159 /* Legal */ 314159E-5L /* Legal */ 510E /* Illegal: incomplete exponent */ 210f /* Illegal: no decimal or exponent */ .e55 /* Illegal: missing integer or fraction */
While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E.
Character Constants
Character literals are enclosed in single quotes e.g., 'x' and can be stored in a simple variable of char type. A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a universal character (e.g., '\u02C0').
There are certain characters in C# when they are preceded by a backslash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here, you have a list of some of such escape sequence codes:
| Escape sequence | Meaning |
|---|---|
| \\ | \ character |
| \' | ' character |
| \" | " character |
| \? | ? character |
| \a | Alert or bell |
| \b | Backspace |
| \f | Form feed |
| \n | Newline |
| \r | Carriage return |
| \t | Horizontal tab |
| \v | Vertical tab |
| \ooo | Octal number of one to three digits |
| \xhh . . . | Hexadecimal number of one or more digits |
String Literals
String literals or constants are enclosed in double quotes "" or with @"". A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters.
You can break a long line into multiple lines using string literals and separating the parts using whitespaces.
Here are some examples of string literals. All the three forms are identical strings.
"hello, dear" "hello, \ dear" "hello, " "d" "ear" @"hello dear"
Defining Constants
Constants are defined using the const keyword. Syntax for defining a constant is:
const <data_type> <constant_name> = value;
C# - Operators
An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. C# is rich in built-in operators and provides the following type of operators:
- Arithmetic Operators
- Relational Operators
- Logical Operators
- Bitwise Operators
- Assignment Operators
- Misc Operators
This tutorial will explain the arithmetic, relational, logical, bitwise, assignment and other operators one by one.
Arithmetic Operators
Following table shows all the arithmetic operators supported by C#. Assume variable A holds 10 and variable B holds 20, then:
| Operator | Description | Example |
|---|---|---|
| + | Adds two operands | A + B will give 30 |
| - | Subtracts second operand from the first | A - B will give -10 |
| * | Multiplies both operands | A * B will give 200 |
| / | Divides numerator by de-numerator | B / A will give 2 |
| % | Modulus Operator and remainder of after an integer division | B % A will give 0 |
| ++ | Increment operator increases integer value by one | A++ will give 11 |
| -- | Decrement operator decreases integer value by one | A-- will give 9 |
Relational Operators
Following table shows all the relational operators supported by C#. Assume variable A holds 10 and variable B holds 20, then:
| Operator | Description | Example |
|---|---|---|
| == | Checks if the values of two operands are equal or not, if yes then condition becomes true. | (A == B) is not true. |
| != | Checks if the values of two operands are equal or not, if values are not equal then condition becomes true. | (A != B) is true. |
| > | Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. | (A > B) is not true. |
| < | Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. | (A < B) is true. |
| >= | Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. | (A >= B) is not true. |
| <= | Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. | (A <= B) is true. |
Logical Operators
Following table shows all the logical operators supported by C#. Assume variable A holds Boolean value true and variable B holds Boolean value false, then:
| Operator | Description | Example |
|---|---|---|
| && | Called Logical AND operator. If both the operands are non zero then condition becomes true. | (A && B) is false. |
| || | Called Logical OR Operator. If any of the two operands is non zero then condition becomes true. | (A || B) is true. |
| ! | Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false. | !(A && B) is true. |
Bitwise Operators
| Operator | Description | Example |
|---|---|---|
| & | Binary AND Operator copies a bit to the result if it exists in both operands. | (A & B) will give 12, which is 0000 1100 |
| | | Binary OR Operator copies a bit if it exists in either operand. | (A | B) will give 61, which is 0011 1101 |
| ^ | Binary XOR Operator copies the bit if it is set in one operand but not both. | (A ^ B) will give 49, which is 0011 0001 |
| ~ | Binary Ones Complement Operator is unary and has the effect of 'flipping' bits. | (~A ) will give -61, which is 1100 0011 in 2's complement form due to a signed binary number. |
| << | Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand. | A << 2 will give 240, which is 1111 0000 |
| >> | Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand. | A >> 2 will give 15, which is 0000 1111 |
Assignment Operators
There are following assignment operators supported by C#:
| Operator | Description | Example |
|---|---|---|
| = | Simple assignment operator, Assigns values from right side operands to left side operand | C = A + B will assign value of A + B into C |
| += | Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand | C += A is equivalent to C = C + A |
| -= | Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand | C -= A is equivalent to C = C - A |
| *= | Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand | C *= A is equivalent to C = C * A |
| /= | Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand | C /= A is equivalent to C = C / A |
| %= | Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand | C %= A is equivalent to C = C % A |
| <<= | Left shift AND assignment operator | C <<= 2 is same as C = C << 2 |
| >>= | Right shift AND assignment operator | C >>= 2 is same as C = C >> 2 |
| &= | Bitwise AND assignment operator | C &= 2 is same as C = C & 2 |
| ^= | bitwise exclusive OR and assignment operator | C ^= 2 is same as C = C ^ 2 |
| |= | bitwise inclusive OR and assignment operator | C |= 2 is same as C = C | 2 |
Misc Operators
There are few other important operators including sizeof, typeof and ? : supported by C#.
| Operator | Description | Example |
|---|---|---|
| sizeof() | Returns the size of a data type. | sizeof(int), will return 4. |
| typeof() | Returns the type of a class. | typeof(StreamReader); |
| & | Returns the address of an variable. | &a; will give actual address of the variable. |
| * | Pointer to a variable. | *a; will pointer to a variable. |
| ? : | Conditional Expression | If Condition is true ? Then value X : Otherwise value Y |
| is | Determines whether an object is of a certain type. | If( Ford is Car) // checks if Ford is an object of the Car class. |
| as | Cast without raising an exception if the cast fails. | Object obj = new StringReader("Hello"); StringReader r = obj as StringReader; |
Operators Precedence in C#
Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator:
For example x = 7 + 3 * 2; here x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7.
Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.
| Category | Operator | Associativity |
|---|---|---|
| Postfix | () [] -> . ++ - - | Left to right |
| Unary | + - ! ~ ++ - - (type)* & sizeof | Right to left |
| Multiplicative | * / % | Left to right |
| Additive | + - | Left to right |
| Shift | << >> | Left to right |
| Relational | < <= > >= | Left to right |
| Equality | == != | Left to right |
| Bitwise AND | & | Left to right |
| Bitwise XOR | ^ | Left to right |
| Bitwise OR | | | Left to right |
| Logical AND | && | Left to right |
| Logical OR | || | Left to right |
| Conditional | ?: | Right to left |
| Assignment | = += -= *= /= %=>>= <<= &= ^= |= | Right to left |
| Comma | , | Left to right |
C# - Decision Making
Decision making structures require that the programmer specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.
Following is the general from of a typical decision making structure found in most of the programming languages:
C# provides following types of decision making statements. Click the following links to check their detail.
| Statement | Description |
|---|---|
| if statement | An if statement consists of a boolean expression followed by one or more statements. |
| if...else statement | An if statement can be followed by an optional else statement, which executes when the boolean expression is false. |
| nested if statements | You can use one if or else if statement inside another if or else if statement(s). |
| switch statement | A switch statement allows a variable to be tested for equality against a list of values. |
| nested switch statements | You can use one switch statement inside another switchstatement(s). |
C# - Loops
There may be a situation, when you need to execute a block of code several number of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.
Programming languages provide various control structures that allow for more complicated execution paths.
A loop statement allows us to execute a statement or group of statements multiple times and following is the general from of a loop statement in most of the programming languages:
C# provides following types of loop to handle looping requirements. Click the following links to check their detail.
| Loop Type | Description |
|---|---|
| while loop | Repeats a statement or group of statements until a given condition is true. It tests the condition before executing the loop body. |
| for loop | Executes a sequence of statements multiple times and abbreviates the code that manages the loop variable. |
| do...while loop | Like a while statement, except that it tests the condition at the end of the loop body |
| nested loops | You can use one or more loop inside any another while, for or do..while loop. |
Loop Control Statements:
Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed.
C# provides the following control statements. Click the following links to check their detail.
| Control Statement | Description |
|---|---|
| break statement | Terminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch. |
| continue statement | Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating. |
C# - Encapsulation
Encapsulation is defined 'as the process of enclosing one or more items within a physical or logical package'. Encapsulation, in object oriented programming methodology, prevents access to implementation details.
Abstraction and encapsulation are related features in object oriented programming. Abstraction allows making relevant information visible and encapsulation enables a programmer to implement the desired level of abstraction.
Encapsulation is implemented by using access specifiers. An access specifier defines the scope and visibility of a class member. C# supports the following access specifiers:
- Public
- Private
- Protected
- Internal
- Protected internal
Public Access Specifier
Public access specifier allows a class to expose its member variables and member functions to other functions and objects. Any public member can be accessed from outside the class.
The following example illustrates this:
using System; namespace RectangleApplication { class Rectangle { //member variables public double length; public double width; public double GetArea() { return length * width; } public void Display() { Console.WriteLine("Length: {0}", length); Console.WriteLine("Width: {0}", width); Console.WriteLine("Area: {0}", GetArea()); } }//end class Rectangle class ExecuteRectangle { static void Main(string[] args) { Rectangle r = new Rectangle(); r.length = 4.5; r.width = 3.5; r.Display(); Console.ReadLine(); } } }
When the above code is compiled and executed, it produces the following result:
Length: 4.5 Width: 3.5 Area: 15.75
In the preceding example, the member variables length and width are declared public, so they can be accessed from the function Main() using an instance of the Rectangle class, named r.
The member function Display() and GetArea() can also access these variables directly without using any instance of the class.
The member functions Display() is also declared public, so it can also be accessed from Main() using an instance of the Rectangle class, named r.
Private Access Specifier
Private access specifier allows a class to hide its member variables and member functions from other functions and objects. Only functions of the same class can access its private members. Even an instance of a class cannot access its private members.
The following example illustrates this:
using System; namespace RectangleApplication { class Rectangle { //member variables private double length; private double width; public void Acceptdetails() { Console.WriteLine("Enter Length: "); length = Convert.ToDouble(Console.ReadLine()); Console.WriteLine("Enter Width: "); width = Convert.ToDouble(Console.ReadLine()); } public double GetArea() { return length * width; } public void Display() { Console.WriteLine("Length: {0}", length); Console.WriteLine("Width: {0}", width); Console.WriteLine("Area: {0}", GetArea()); } }//end class Rectangle class ExecuteRectangle { static void Main(string[] args) { Rectangle r = new Rectangle(); r.Acceptdetails(); r.Display(); Console.ReadLine(); } } }
When the above code is compiled and executed, it produces the following result:
Enter Length: 4.4 Enter Width: 3.3 Length: 4.4 Width: 3.3 Area: 14.52
In the preceding example, the member variables length and width are declared private, so they cannot be accessed from the function Main(). The member functions AcceptDetails() and Display() can access these variables. Since the member functions AcceptDetails() and Display() are declared public, they can be accessed from Main() using an instance of the Rectangle class, named r.
Protected Access Specifier
Protected access specifier allows a child class to access the member variables and member functions of its base class. This way it helps in implementing inheritance. We will discuss this in more details in the inheritance chapter.
Internal Access Specifier
Internal access specifier allows a class to expose its member variables and member functions to other functions and objects in the current assembly. In other words, any member with internal access specifier can be accessed from any class or method defined within the application in which the member is defined.
The following program illustrates this:
using System; namespace RectangleApplication { class Rectangle { //member variables internal double length; internal double width; double GetArea() { return length * width; } public void Display() { Console.WriteLine("Length: {0}", length); Console.WriteLine("Width: {0}", width); Console.WriteLine("Area: {0}", GetArea()); } }//end class Rectangle class ExecuteRectangle { static void Main(string[] args) { Rectangle r = new Rectangle(); r.length = 4.5; r.width = 3.5; r.Display(); Console.ReadLine(); } } }
When the above code is compiled and executed, it produces the following result:
Length: 4.5 Width: 3.5 Area: 15.75
In the preceding example, notice that the member function GetArea() is not declared with any access specifier. Then what would be the default access specifier of a class member if we don't mention any? It is private.
Protected Internal Access Specifier
The protected internal access specifier allows a class to hide its member variables and member functions from other class objects and functions, except a child class within the same application. This is also used while implementing inheritance.
class Tester { static void Main(string[] args) { Transaction t1 = new Transaction("001", "8/10/2012", 78900.00); Transaction t2 = new Transaction("002", "9/10/2012", 451900.00); t1.showTransaction(); t2.showTransaction(); Console.ReadKey(); } } }
When the above code is compiled and executed, it produces the following result:
Transaction: 001 Date: 8/10/2012 Amount: 78900 Transaction: 002 Date: 9/10/2012 Amount: 451900
C# - Namespaces
A namespace is designed for providing a way to keep one set of names separate from another. The class names declared in one namespace will not conflict with the same class names declared in another.
Defining a Namespace
A namespace definition begins with the keyword namespace followed by the namespace name as follows:
namespace namespace_name { // code declarations }
To call the namespace-enabled version of either function or variable, prepend the namespace name as follows:
namespace_name.item_name;
The following program demonstrates use of namespaces:
using System; namespace first_space { class namespace_cl { public void func() { Console.WriteLine("Inside first_space"); } } } namespace second_space { class namespace_cl { public void func() { Console.WriteLine("Inside second_space"); } } } class TestClass { static void Main(string[] args) { first_space.namespace_cl fc = new first_space.namespace_cl(); second_space.namespace_cl sc = new second_space.namespace_cl(); fc.func(); sc.func(); Console.ReadKey(); } }
When the above code is compiled and executed, it produces the following result:
Inside first_space Inside second_space
The using Keyword
The using keyword states that the program is using the names in the given namespace. For example, we are using the System namespace in our programs. The class Console is defined there. We just write:
Console.WriteLine ("Hello there");
We could have written the fully qualified name as:
System.Console.WriteLine("Hello there");
You can also avoid prepending of namespaces with the using namespace directive. This directive tells the compiler that the subsequent code is making use of names in the specified namespace. The namespace is thus implied for the following code:
Let us rewrite our preceding example, with using directive:
using System; using first_space; using second_space; namespace first_space { class abc { public void func() { Console.WriteLine("Inside first_space"); } } } namespace second_space { class efg { public void func() { Console.WriteLine("Inside second_space"); } } } class TestClass { static void Main(string[] args) { abc fc = new abc(); efg sc = new efg(); fc.func(); sc.func(); Console.ReadKey(); } }
When the above code is compiled and executed, it produces the following result:
Inside first_space Inside second_space
C# - Preprocessor Directives
The preprocessors directives give instruction to the compiler to preprocess the information before actual compilation starts.
All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. Preprocessor directives are not statements, so they do not end with a semicolon (;).
C# compiler does not have a separate preprocessor; however, the directives are processed as if there was one. In C# the preprocessor directives are used to help in conditional compilation. Unlike C and C++ directives, they are not used to create macros. A preprocessor directive must be the only instruction on a line.
List of Preprocessor Directives in C#
The following table lists the preprocessor directives available in C#:
| Preprocessor Directive | Description. |
|---|---|
| #define | It defines a sequence of characters, called symbol. |
| #undef | It allows you to undefine a symbol. |
| #if | It allows testing a symbol or symbols to see if they evaluate to true. |
| #else | It allows to create a compound conditional directive, along with #if. |
| #elif | It allows creating a compound conditional directive. |
| #endif | Specifies the end of a conditional directive. |
| #line | It lets you modify the compiler's line number and (optionally) the file name output for errors and warnings. |
| #error | It allows generating an error from a specific location in your code. |
| #warning | It allows generating a level one warning from a specific location in your code. |
| #region | It lets you specify a block of code that you can expand or collapse when using the outlining feature of the Visual Studio Code Editor. |
| #endregion | It marks the end of a #region block. |
The #define Preprocessor
The #define preprocessor directive creates symbolic constants.
#define lets you define a symbol, such that, by using the symbol as the expression passed to the #if directive, the expression will evaluate to true. Its syntax is as follows:
#define symbol
The following program illustrates this:
#define PI using System; namespace PreprocessorDAppl { class Program { static void Main(string[] args) { #if (PI) Console.WriteLine("PI is defined"); #else Console.WriteLine("PI is not defined"); #endif Console.ReadKey(); } } }
When the above code is compiled and executed, it produces the following result:
PI is defined
Conditional Directives
You can use the #if directive to create a conditional directive. Conditional directives are useful for testing a symbol or symbols to see if they evaluate to true. If they do evaluate to true, the compiler evaluates all the code between the #if and the next directive.
Syntax for conditional directive is:
#if symbol [operator symbol]...
Where, symbol is the name of the symbol you want to test. You can also use true and false or prepend the symbol with the negation operator.
The operator symbol is the operator used for evaluating the symbol. Operators could be either of the following:
- == (equality)
- != (inequality)
- && (and)
- || (or)
You can also group symbols and operators with parentheses. Conditional directives are used for compiling code for a debug build or when compiling for a specific configuration. A conditional directive beginning with a #if directive must explicitly be terminated with a #endif directive.
The following program demonstrates use of conditional directives:
#define DEBUG #define VC_V10 using System; public class TestClass { public static void Main() { #if (DEBUG && !VC_V10) Console.WriteLine("DEBUG is defined"); #elif (!DEBUG && VC_V10) Console.WriteLine("VC_V10 is defined"); #elif (DEBUG && VC_V10) Console.WriteLine("DEBUG and VC_V10 are defined"); #else Console.WriteLine("DEBUG and VC_V10 are not defined"); #endif Console.ReadKey(); } }
When the above code is compiled and executed, it produces the following result:
DEBUG and VC_V10 are defined
C# - Regular Expressions
A regular expression is a pattern that could be matched against an input text. The .Net framework provides a regular expression engine that allows such matching. A pattern consists of one or more character literals, operators, or constructs.
Constructs for Defining Regular Expressions
There are various categories of characters, operators, and constructs that lets you to define regular expressions. Click the follwoing links to find these constructs.
The Regex Class
The Regex class is used for representing a regular expression.
The Regex class has the following commonly used methods:
| S.N | Methods & Description |
|---|---|
| 1 | public bool IsMatch( string input ) Indicates whether the regular expression specified in the Regex constructor finds a match in a specified input string. |
| 2 | public bool IsMatch( string input, int startat ) Indicates whether the regular expression specified in the Regex constructor finds a match in the specified input string, beginning at the specified starting position in the string. |
| 3 | public static bool IsMatch( string input, string pattern ) Indicates whether the specified regular expression finds a match in the specified input string. |
| 4 | public MatchCollection Matches( string input ) Searches the specified input string for all occurrences of a regular expression. |
| 5 | public string Replace( string input, string replacement ) In a specified input string, replaces all strings that match a regular expression pattern with a specified replacement string. |
| 6 | public string[] Split( string input ) Splits an input string into an array of substrings at the positions defined by a regular expression pattern specified in the Regex constructor. |
For the complete list of methods and properties, please read the Microsoft documentation on C#.
Example 1
The following example matches words that start with 'S':
using System; using System.Text.RegularExpressions; namespace RegExApplication { class Program { private static void showMatch(string text, string expr) { Console.WriteLine("The Expression: " + expr); MatchCollection mc = Regex.Matches(text, expr); foreach (Match m in mc) { Console.WriteLine(m); } } static void Main(string[] args) { string str = "A Thousand Splendid Suns"; Console.WriteLine("Matching words that start with 'S': "); showMatch(str, @"\bS\S*"); Console.ReadKey(); } } }
When the above code is compiled and executed, it produces the following result:
Matching words that start with 'S': The Expression: \bS\S* Splendid Suns
C# - Exception Handling
An exception is a problem that arises during the execution of a program. A C# exception is a response to an exceptional circumstance that arises while a program is running, such as an attempt to divide by zero.
Exceptions provide a way to transfer control from one part of a program to another. C# exception handling is built upon four keywords: try, catch, finally and throw.
- try: A try block identifies a block of code for which particular exceptions will be activated. It's followed by one or more catch blocks.
- catch: A program catches an exception with an exception handler at the place in a program where you want to handle the problem. The catch keyword indicates the catching of an exception.
- finally: The finally block is used to execute a given set of statements, whether an exception is thrown or not thrown. For example, if you open a file, it must be closed whether an exception is raised or not.
- throw: A program throws an exception when a problem shows up. This is done using a throw keyword.
Syntax
Assuming a block will raise and exception, a method catches an exception using a combination of the try and catch keywords. A try/catch block is placed around the code that might generate an exception. Code within a try/catch block is referred to as protected code, and the syntax for using try/catch looks like the following:
try { // statements causing exception } catch( ExceptionName e1 ) { // error handling code } catch( ExceptionName e2 ) { // error handling code } catch( ExceptionName eN ) { // error handling code } finally { // statements to be executed }
You can list down multiple catch statements to catch different type of exceptions in case your try block raises more than one exception in different situations.
Exception Classes in C#
C# exceptions are represented by classes. The exception classes in C# are mainly directly or indirectly derived from the System.Exception class. Some of the exception classes derived from the System.Exception class are the System.ApplicationException and System.SystemException classes.
The System.ApplicationException class supports exceptions generated by application programs. So the exceptions defined by the programmers should derive from this class.
The System.SystemException class is the base class for all predefined system exception.
The following table provides some of the predefined exception classes derived from the Sytem.SystemException class:
| Exception Class | Description |
|---|---|
| System.IO.IOException | Handles I/O errors. |
| System.IndexOutOfRangeException | Handles errors generated when a method refers to an array index out of range. |
| System.ArrayTypeMismatchException | Handles errors generated when type is mismatched with the array type. |
| System.NullReferenceException | Handles errors generated from deferencing a null object. |
| System.DivideByZeroException | Handles errors generated from dividing a dividend with zero. |
| System.InvalidCastException | Handles errors generated during typecasting. |
| System.OutOfMemoryException | Handles errors generated from insufficient free memory. |
| System.StackOverflowException | Handles errors generated from stack overflow. |
Handling Exceptions
C# provides a structured solution to the exception handling problems in the form of try and catch blocks. Using these blocks the core program statements are separated from the error-handling statements.
These error handling blocks are implemented using the try, catch and finally keywords. Following is an example of throwing an exception when dividing by zero condition occurs:
using System; namespace ErrorHandlingApplication { class DivNumbers { int result; DivNumbers() { result = 0; } public void division(int num1, int num2) { try { result = num1 / num2; } catch (DivideByZeroException e) { Console.WriteLine("Exception caught: {0}", e); } finally { Console.WriteLine("Result: {0}", result); } } static void Main(string[] args) { DivNumbers d = new DivNumbers(); d.division(25, 0); Console.ReadKey(); } } }
When the above code is compiled and executed, it produces the following result:
Exception caught: System.DivideByZeroException: Attempted to divide by zero. at ... Result: 0
C# - File I/O
A file is a collection of data stored in a disk with a specific name and a directory path. When a file is opened for reading or writing, it becomes a stream.
The stream is basically the sequence of bytes passing through the communication path. There are two main streams: the input stream and the output stream. The input stream is used for reading data from file (read operation) and the output stream is used for writing into the file (write operation).
C# I/O Classes
The System.IO namespace has various class that are used for performing various operation with files, like creating and deleting files, reading from or writing to a file, closing a file etc.
The following table shows some commonly used non-abstract classes in the System.IO namespace:
| I/O Class | Description |
|---|---|
| BinaryReader | Reads primitive data from a binary stream. |
| BinaryWriter | Writes primitive data in binary format. |
| BufferedStream | A temporary storage for a stream of bytes. |
| Directory | Helps in manipulating a directory structure. |
| DirectoryInfo | Used for performing operations on directories. |
| DriveInfo | Provides information for the drives. |
| File | Helps in manipulating files. |
| FileInfo | Used for performing operations on files. |
| FileStream | Used to read from and write to any location in a file. |
| MemoryStream | Used for random access to streamed data stored in memory. |
| Path | Performs operations on path information. |
| StreamReader | Used for reading characters from a byte stream. |
| StreamWriter | Is used for writing characters to a stream. |
| StringReader | Is used for reading from a string buffer. |
| StringWriter | Is used for writing into a string buffer. |
The FileStream Class
The FileStream class in the System.IO namespace helps in reading from, writing to and closing files. This class derives from the abstract class Stream.
You need to create a FileStream object to create a new file or open an existing file. The syntax for creating a FileStream object is as follows:
FileStream <object_name> = new FileStream( <file_name>, <FileMode Enumerator>, <FileAccess Enumerator>, <FileShare Enumerator>);
For example, for creating a FileStream object F for reading a file named sample.txt:
FileStream F = new FileStream("sample.txt", FileMode.Open, FileAccess.Read, FileShare.Read);
| Parameter | Description |
|---|---|
| FileMode |
The FileMode enumerator defines various methods for opening files. The members of the FileMode enumerator are:
|
| FileAccess |
FileAccess enumerators have members: Read, ReadWrite and Write.
|
| FileShare |
FileShare enumerators have the following members:
|
Example:
The following program demonstrates use of the FileStream class:
using System; using System.IO; namespace FileIOApplication { class Program { static void Main(string[] args) { FileStream F = new FileStream("test.dat", FileMode.OpenOrCreate, FileAccess.ReadWrite); for (int i = 1; i <= 20; i++) { F.WriteByte((byte)i); } F.Position = 0; for (int i = 0; i <= 20; i++) { Console.Write(F.ReadByte() + " "); } F.Close(); Console.ReadKey(); } } }
When the above code is compiled and executed, it produces the following result:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 -1
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