Control Statement

1 if Statement

The if statement is a control statement that executes a block of code

if an expression evaluates to true. It takes this form:

if (expression)

statement1

else

statement2

where

• expression is an expression that can be implicitly converted to bool or

a type

that contains overloading of the true and false operators

• statement1 is the embedded statement(s) to be executed if expression is true

• statement2 is the embedded statement(s) to be executed if expression is false

Note that unlike C++, C# and Java do not allow the expression to be

evaluated to 1 or 0. That is, the integer 1 does not stand for true, and 0 does

not stand for false.

Example:

int a=1;

if(a==i)

{

response.write("The integer value is One"); 

}

else

{

response.write("The integer value is not One"); 

}

2 The while Loop

The while statement executes a statement or a block of statements until a

specified expression evaluates to false. It takes this form:

while (expression) statement where 

• expression is an expression that can be implicitly converted to bool or a type

that contains overloading of the true and false operators. The expression is

used to test the loop-termination criteria.

• statement is the embedded statement(s) to be executed.

Because the test of expression takes place before each execution of the loop,

a while loop executes zero or more times. A while loop can be terminated

when a break, goto, return, or throw statement transfers control outside the

loop. To pass control to the next iteration without exiting the loop, you

use the continue statement.

while loops can be nested. In nested while loops, a break or a goto statement

in the innermost loop merely transfers control to the outer loop. A return

statement exits from the outermost loop, and a throw statement exits from the

outer loop depending on whether the thrown exception gets caught or

ignored. Listing 5.1 shows the while loop in action.

Listing 1 C# while Loop

using System;

public class Test {

  public static void Main(string[] args) {

    int i = 0;

    int j = 0;

    while (j < 5) {

      Console.WriteLine("j "+j);    

 while (i < 8) {

        Console.WriteLine("i "+i);

        ++i;

        j +=10;

      }

    }

  }

}

3 The do while Loop

The  do  while  statement  executes  a  statement  or  a  block  of  statements repeatedly  until  a  specified  expression  evaluates  to  false.  It  takes  the following form:

do statement while (expression);

 <<Code>>

where 

<<Condition>>

     expression  is  an  expression  that  can  be  implicitly  converted  to  bool  or  a type  that  contains  overloading  of  the  true  and  false  operators.  The expression is used to test the loop-termination criteria.

    statement is the embedded statement(s) to be executed. Unlike the while statement, the body loop of the do statement is executed

at least once regardless of the value of the expression. 

4 The for Loop 

he for loop executes a statement or a block of statements repeatedly until a specified expression evaluates to false. It takes the following form:

for ([initializers]; [expression]; [iterators]) statement

where

     initializers  is  a  comma-separated  list  of  expressions  or  assignment

statements to initialize the loop counters.

     expression  is  an  expression  that  can  be 

 implicitly  converted  to  bool  or  a type  that  contains  overloading  of  the  true  and  false  operators.  The

expression is used to test the loop-termination criteria.

     iterators  are  expression  statements  to  increment  or  decrement  the  loop counters.

    statement is the embedded statement(s) to be executed. 

The for statement executes the statement repeatedly as follows:

1.   The initializers are evaluated.

2.   While the expression evaluates to true, the statement(s) are executed and the iterators are evaluated.

3.   When  the  expression  becomes  false,  control  is  transferred  outside  the loop