Subject : Structured Programming Approach

Title : Control Structures

Marks : 10M

C language supports the following statements known as control or decision making statements.

1. if statement
2. switch statement
3. Conditional operator statement
4. goto statement

if Statement

The if statement is used to control the flow of execution of statements and is of the form

if(test expression) 
Statement;

It allows the computer to evaluate the expression first and then, depending on whether the value of the expression is ‘true’ or ‘false’, it transfers the control to a particular statement. Eg: if(bank balance is zero)

Borrow money;

The If…else Statement

The if….else statement is an extension of simple if statement.The general form is

 if(test expression) 
{ 
True-block statement(s) 
 } 
else
{ 
False-block statement(s) 
} 
statement-x

If the test expression is true, then the true block statements are executed; otherwise the false block statement will be executed.

Nesting Of If…..else Statements

When a series of decisions are involved, we may have to use more than one if….else statements, in nested form as follows.

 if(test condition 1)

 { 
 if(test condition 2) 
 { 
  statement-1; 
 } 
 else

{ 
  statement-2; 
} 
}

else { statement-3; } statement-x;

The Elseif Ladder

The general form is

if(condn 1)
statement-1; 
else if (condn 2) 
statement-2; 
else if (condn 3) 
statement-3; 
else if (condn n) 
statement-n; 
else 
default statement; 
statement-x;

The Switch Statement

Switch statement is used for complex programs when the number of alternatives increases. The switch statement tests the value of the given variable against the list of case values and when a match is found, a block of statements associated with that case is executed.

The general form of switch statement is

switch(expression) 
{ 
case value-1: 
block-1 

break; 
case value-2: 
block-2 

break; 
……. 
……. 
default: 
} 
statement-x;