islower in C Programming

The C islower function is one of the Standard Library Functions available in this C programming language. This function is used to check whether the given character is a lowercase alphabet or not. Let us see an example of how to use islower in C Programming language.

islower Syntax

The C Programming islower is a built-in function present in the header file used to check whether the character is a lowercase alphabet or not and its syntax.

islower(char)

The above islower function will accept a single character as the parameter and check whether the given character is in lowercase or not. The islower function will return an integer value as output.

  • If the character inside the function is in lowercase, then it will return non zero value
  • If the character inside the function is not in lowercase, it will return 0

islower in C Programming Example

The islower method is used to find whether the given character is a lowercase character or not.

This program allows the user to enter any character and check whether the character is between a to z using the islower function.

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

int main()
{
    char ch;
    printf("Please Enter Any Lowercase Character: \n");
    scanf("%c", &ch);

    if(islower(ch))
    {
      printf("\n You have entered a Lowercase Character");         
    }
    else
    {
      printf("\n %c is not a Lowercase Alphabet", ch);
      printf("\n I request you to enter Valid Lowercase Character");	
    }
}
islower in C Programming 1

Let me enter the Uppercase letter.

Please Enter Any Lowercase Character: 
T

 T is not a Lowercase Alphabet
 I request you to enter Valid Lowercase Character

First, we declared a character variable called ch.

char ch;

The following statement will ask the user to enter any character. And then, we are using the C Programming scanf to assign the user entered a character to ch variable.

printf("Please Enter Any Lowercase Character: \n");
scanf("%c", &ch);

In this next line, we added the If Statement to check whether the character is between ‘a’ and ‘z’ or not using C islower function. If the condition is True, then the following statement will print

printf("\n You have entered a Lowercase Character");

If the above condition is FALSE, the given character is not a lowercase Alphabet. So, it will print the below statements.

printf("\n %c is not a Lowercase Alphabet", ch);
printf("\n I request you to enter Valid Lowercase Character");

The above code will definitely check whether the given character is a lowercase character or not, but what if we enter the numeric value? Please refer C Program to check whether the Character is Lowercase or Not article. It helps you know how to check whether the character is lowercase or not without using the islower function.

Please Enter Any Lowercase Character: 
8

 8 is not a Lowercase Alphabet
 I request you to enter Valid Lowercase Character