The first line of the program using System; the using keyword is used to include the System namespace in the program. A program generally has multiple using statements.

The next line has the namespace declaration. A namespace is a collection of classes. The “Hello World” Application namespace contains the class Hello World.

The next line has a class declaration, the class Hello World 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 Hello World class has only one method Main.

The next line defines the Main method, which is the entry point for all C# programs. The Main method states what the class will do when executed

The next line /*...*/ will be ignored by the compiler and it has been put to add additional comments 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 naote 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.

C# Type Conversion Methods: C# provides the following built-in type conversion methods:

S.N Methods & Description

1 ToBooleanConverts a type to a Boolean value, where possible.

2 ToByteConverts a type to a byte.

3 ToCharConverts a type to a single Unicode character, where possible.

4 ToDateTimeConverts a type (integer or string type) to date-time structures.

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5 ToDecimalConverts a floating point or integer type to a decimal type.

6 ToDoubleConverts a type to a double type.

7 ToInt16Converts a type to a 16-bit integer.

8 ToInt32Converts a type to a 32-bit integer.

9 ToInt64Converts a type to a 64-bit integer.

10 ToSbyteConverts a type to a signed byte type.

11 ToSingleConverts a type to a small floating point number.

12 ToStringConverts a type to a string.

13 ToTypeConverts a type to a specified type.

14 ToUInt16Converts a type to an unsigned int type.

15 ToUInt32Converts a type to an unsigned long type.

16 ToUInt64Converts a type to an unsigned big integer.

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.

Arithmetic Operators:

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:

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Operator Description Examp

le

== 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:

Operator Description Examp

le

&& 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.

Conditions:

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).

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C# - Loops: A loop statement allows us to execute a statement or group of statements multiple times .

Loop Type Description

while loop Repeats a statement or group of statements while 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.

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# - Arrays:

An array stores a fixed-size sequential collection of elements of the same type. An array is used to store a

collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

Instead of declaring individual variables, such as number0, number1, ..., and number99, you declare one array

variable such as numbers and use numbers[0], numbers[1], and ..., numbers[99] to represent individual variables.

A specific element in an array is accessed by an index.

Declaring Arrays:

To declare an array in C#, you can use the following syntax:

datatype[] arrayName;

where,

datatype is used to specify the type of elements to be stored in the array. [ ] specifies the rank of the array. The rank specifies the size of the array. arrayName specifies the name of the array.

For example,

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double[] balance;

Initializing an Array

Array is a reference type, so you need to use the new keyword to create an instance of the array.

For example,

double[] balance = new double[10];

Code Description

abstractThe abstract modifier can be used with classes, methods, properties, indexers, and events.

as The as operator is used to perform conversions between compatible types.

base The base keyword is used to access members of the base class from within a derived class

bool The bool keyword is an alias of System.Boolean. It is used to declare variables to store the Boolean values, true and false.

break The keyword break is used to exit out of a loop or switch block.byte It represents an 8-bit unsigned integer whose value ranges from 0 to 255.case case is often used in a switch statement.

catch The keyword catch is used to identify a statement or statement block for execution

char It represents a Unicode character whose from 0 to 65,535.

checkedThe checked keyword is used to control the overflow-checking context for integral-type arithmetic operations and conversions.

class The class keyword is used to declare a class.

constThe const keyword is used in field and local variable declarations to make the variable constant

continue Its affect is to end the current loop  and proceed to the next one.decimal The decimal keyword denotes a 128-bit data type.default The default keyword can be used in the switch statement

delegateThe delegate keyword is used to declare a delegate. A delegate is a

programming construct that is used to obtain a callable reference to a method of

a class.

doThe do statement executes a statement or a block of statements repeatedly until a specified expression evaluates to false.

doubleThe double keyword denotes a simple type that stores 64-bit floating-point values.

elseAn else clause immediately follows an if-body. It provides code to execute when the condition is false. 

enumThe enum keyword is used to declare an enumeration, a distinct type consisting of a set of named constants called the enumerator list.

event It is used to declare an event.

explicitThe explicit keyword is used to declare an explicit user-defined type conversion operator

externUse the extern modifier in a method declaration to indicate that the method is implemented externally.

false The false keyword is a boolean constant valuefinally The finally block is useful for cleaning up any resources allocated in the try block.fixed Prevents relocation of a variable by the garbage collector.float The float keyword denotes a simple type that stores 32-bit floating-point values.

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forThe for loop executes a statement or a block of statements repeatedly until a specified expression evaluates to false.

foreachThe foreach statement repeats a group of embedded statements for each element in an array or an object collection.

goto The goto statement transfers the program control directly to a labeled statement.

ifThe if statement selects a statement for execution based on the value of a Boolean expression.

implicitThe implicit keyword is used to declare an implicit user-defined type conversion operator.

in The in keyword identifies the collection to enumerate in a foreach   loop .

intThe int keyword denotes an integral type that stores values according to the size and range

interfaceThe interface keyword is used to declare an interface. Interfaces provide a construct for a programmer to create types that can have methods, properties, delegates, events, and indexers declared, but not implemented.

internalThe internal keyword is an access modifier for types and type members. That is, it is only visible within the assembly that implements it.

isThe is operator is used to check whether the run-time type of an object is compatible with a given type.  Using is on a null variable always returns false.

lockThe lock keyword marks a statement block as a critical section by obtaining the mutual-exclusion lock for a given object, executing a statement, and then releasing the lock.

longThe long keyword denotes an integral type that stores values according to the size and range.That is, it represents a 64-bit signed integer whose value ranges from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807.

namespaceThe namespace keyword is used to supply a namespace for class, structure, and type declarations.

new In C#, the new keyword can be used as an operator or as a modifier.

nullThe null keyword is a literal that represents a null reference, one that does not refer to any object.

object  It represents the base class from which all other reference types derive.

operatorThe operator keyword is used to declare an operator in a class or struct declaration.

outThe out method parameter keyword on a method parameter causes a method to refer to the same variable that was passed into the method

overrideUse the override modifier to modify a method, a property, an indexer, or an event.

paramsThe keyword params is used to describe when a grouping of parameters are passed to a method, but the number of parameters are not important, as they may vary.

private To make the field, method, or property private to its enclosing class. That is, it is not visible outside of its class.

protected To make the field, method, or property protected to its enclosing class. That is, it is not visible outside of its class.

public To make the field, method, or property public to its enclosing class. That is, it is visible from any class.

readonly The readonly keyword is a modifier that you can use on fields.

refThe ref keyword explicitely specifies that a variable should be passed by reference rather than by value.

returnThe return statement terminates execution of the method in which it appears and returns control to the calling method.

sbyte  It represents an 8-bit signed integer whose value ranges from -128 to 127.

sealed A sealed class cannot be inherited.short It represents a 16-bit signed integer whose value ranges from -32,768 to 32,767.sizeof The sizeof keyword returns how many bytes an object requires to be stored.

stackalloc Allocates a block of memory on the stack.

staticUse the static modifier to declare a static member, which belongs to the type itself rather than to a specific object.

string The string type represents a string of Unicode characters.

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structA struct type is a value type that can contain constructors, constants, fields, methods, properties, indexers, operators, events, and nested types.

switchThe switch statement is a control statement that handles multiple selections by passing control to one of the case statements within its body.

thisThe this keyword refers to the current instance of the class. Static member functions do not have a this pointer.

throwThe throw statement is used to signal the occurrence of an anomalous situation (exception) during the program execution.

true In C#, the true keyword can be used as an overloaded operator or as a literal.

tryThe try-catch statement consists of a try block followed by one or more catchclauses, which specify handlers for different exceptions.

typeof The typeof operator is used to obtain the System.Type object for a type.

uintThe uint keyword denotes an integral type that stores values according to the size and range shown in the following table.

ulongThe ulong keyword denotes an integral type that stores values according to the size and range shown in the following table.

uncheckedThe unchecked keyword is used to control the overflow-checking context for integral-type arithmetic operations and conversions.

unsafeThe unsafe keyword denotes an unsafe context, which is required for any operation involving pointers.

ushortThe ushort keyword denotes an integral data type that stores values according to the size and range shown in the following table.

using The using keyword has two major uses.

virtualThe virtual keyword is used to modify a method or property declaration, in which case the method or the property is called a virtual member.

volatileThe volatile keyword indicates that a field can be modified in the program by something such as the operating system, the hardware, or a concurrently executing thread.

voidWhen used as the return type for a method, void specifies that the method does not return a value.

whileThe while statement executes a statement or a block of statements until a specified expression evaluates to false.

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