C - If-Else Statements

If Statement

The If statement is used to execute a block of code when the condition is evaluated to be true. When the condition is evaluated to be false, the program will skip the if-code block.

Syntax

if(condition){
  statements;
}

Flow Diagram:

In the example below, the if code block is created which executes only when the variable i is divisible by 3.

#include <stdio.h>
 
int main (){
  int i = 15;
  if (i % 3 == 0) {
    printf("%i is divisible by 3.", i); 
  }

  return 0;
}

The output of the above code will be:

15 is divisible by 3.

If-else Statement

The else statement is always used with if statement. It is used to execute block of codes whenever if condition gives false result.

Syntax

if(condition) {
  statements;
} else {
  statements;
}

Flow Diagram:

In the example below, else statement is used to print a message if the variable i is not divisible by 3.

#include <stdio.h>
 
int main () {
  int i = 16;
  if (i % 3 == 0) {
    printf("%i is divisible by 3.", i);
  } else {
    printf("%i is not divisible by 3.", i);
  }
  return 0;
}

The output of the above code will be:

16 is not divisible by 3.

else if Statement

For adding more conditions, else if statement in used. The program first checks if condition. When found false, it checks else if conditions. If all else if conditions are found false, then else code block is executed.

Syntax

if(condition) {
  statements;
} else if(condition) {
  statements;
}
...
...
...
} else {
  statements;
}

Flow Diagram:

In the example below, else if statement is used to add more conditions between if statement and else statement.

#include <stdio.h>
 
int main (){
  int i = 16;
  if (i > 25) {
    printf("%i is greater than 25.\n", i);
  } else if(i <=25 && i >=10) {
    printf("%i lies between 10 and 25.\n", i);
  } else {
    printf("%i is less than 10.\n", i);
  }
  return 0;
}

The output of the above code will be:

16 lies between 10 and 25.