freeCodeCamp/guide/english/c/if/index.md

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If

If

The if statement executes different blocks of code based on conditions.

if (condition) {
	// Do something when `condition` is true
}
else {
	// Do something when original if `condition` is false
}

When condition is true, code inside the if section executes, otherwise else executes. Sometimes you would need to add a second condition. For readability, you should use a else if rather than nesting if statements.

if (condition) {
	// Do something if `condition` is true
}
else if (anotherCondition) {
	// Do something if `anotherCondition` is true
}
else {
	// Do something if `condition` AND `anotherCondition` is false
}

Note: else and else if sections are not required, while if is mandatory. Furthermore, else and else if can only be used following an if statement. In the instance when one if statement is executed, the following else if and else statements are ignored.

Example

#include <stdio.h>

int main () {

   // Local variable definition
   int a = 100;

   // Check the boolean condition
   if(a < 5) {
      // If condition is true then print the following
      printf("a is less than 5!\n" );
   }
   else {
      // If condition is false then print the following
      printf("a is not less than 5!\n" );
   }

   printf("Value of a is : %d\n", a);

   return 0;
}

Output

-> a is not less than 5!
-> Value of a is : 10

Nested IF Statement

if( boolean_expression 1) {

   /* Executes when the boolean expression 1 is true */
   if(boolean_expression 2) {
      /* Executes when the boolean expression 2 is true */
   }
}

Example

#include <stdio.h>
 
int main () {

   /* local variable definition */
   int a = 100;
   int b = 200;
 
   /* check the boolean condition */
   if( a == 100 ) {
   
      /* if condition is true then check the following */
      if( b == 200 ) {
         /* if condition is true then print the following */
         printf("Value of a is 100 and b is 200\n" );
      }
   }
   
   printf("Exact value of a is : %d\n", a );
   printf("Exact value of b is : %d\n", b );
 
   return 0;
}

for more info visit https://www.tutorialspoint.com/cprogramming/nested_if_statements_in_c.htm