C Library - islower() function

The C ctype library islower() function is used to check whether the passed character is a lowercase letter.

Syntax

Following is the C library syntax of the islower() function −

int islower(int c);

Parameters

This function accepts a single parameter −

• c − This is the character to be checked, passed as an integer. The value must be representable as an unsigned char or the value of EOF.

Return Value

The function returns a non-zero value (true) if c is a lowercase letter ('a' to 'z').It returns 0 (false) if c is not a lowercase letter.

Example 1: Checking Characters

Here islower() checks different types of input like uppercase character, lowercase characters and numbers/digits.

#include <stdio.h>
#include <ctype.h>

int main () {
   int var1 = 'Q';
   int var2 = 'q';
   int var3 = '3';
    
   if( islower(var1) ) {
      printf("var1 = |%c| is lowercase character\n", var1 );
   } else {
      printf("var1 = |%c| is not lowercase character\n", var1 );
   }
   
   if( islower(var2) ) {
      printf("var2 = |%c| is lowercase character\n", var2 );
   } else {
      printf("var2 = |%c| is not lowercase character\n", var2 );
   }
   
   if( islower(var3) ) {
      printf("var3 = |%c| is lowercase character\n", var3 );
   } else {
      printf("var3 = |%c| is not lowercase character\n", var3 );
   }
   
   return(0);
}

Output

The above code produces following result−

var1 = |Q| is not lowercase character
var2 = |q| is lowercase character
var3 = |3| is not lowercase character