C Basics - The if Statement in C

C uses the keyword if to implement the decision control instruction. An if statement consists of a Boolean expression followed by one or more statements.

The syntax of an if statement is,

if(boolean_expression) {
   /* statement(s) will execute if the boolean expression is true */
}

The general form of if statement looks like this:

if ( this condition is true ) 
{
execute statement 1 ; 
execute statement 2 ;
…
execute statement n ;   
}

The condition following the keyword if is always enclosed within a pair of parentheses. If the condition, whatever it is, is true, then the statement is executed. If the condition is not true then the statement is not executed; instead the program skips past it. We express a condition using C’s ‘relational’ operators. An expression can also be used as condition.

Simplified forms:

if ( this condition is true ) 
execute this statement ;
if ( this expression evaluates to true ) 
execute this statement ;

Note that in C a non-zero value is considered to be true, whereas a 0 is considered to be false. The default scope of if is the statement immediately after the if. To override this default scope a pair of braces as shown above.

/* Demonstration of if statement */ 
#include <stdio .h>
int main( ) 
{ 
 int num ; 
 printf ( "\nEnter a number less than 10: " ) ; 
 scanf ( "%d", &num ) ; 

 if ( num < 10 ) 
  printf ( "\nThanks! I got your number %d", num) ; 

 if ( num ) 
  printf ( "\n The number %d is non-zero", num) ;

 if ( num == 0 ) 
  printf ( "\n The number is zero" ) ;

 if ( num >= 10 ) 
  printf ( "\n The number %d is not less than 10", num ) ;

 if ( 3+3/6 ) 
  printf ( "\n The expression 3+3/5 evaluates to non-zero value") ;

 if ( (3+3-6) == 0) 
  printf ( "\n The condition 3+3-6 evaluates to zero") ;

}

Output of above program,

Enter a number less than 10: 3

Thanks! I got your number 3
 The number 3 is non-zero
 The expression 3+3/5 evaluates to non-zero value
 The condition 3+3-6 evaluates to zero

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Related topics:
Overview of Statements in C   |   Decision Making Statements in C   |   The if-else Statement in C   |   The else-if Statement in C   |   Nested if-else Statement in C   |   Forms of if Statement in C   |   Switch Statement in C   |   Conditional Operator Statement in C   |   The null Statement in C

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List of topics: C Programming

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