islower() Function Example in C Programming

In this source code example, we will see how to use the islower() function in C programming with an example.

islower() Function Overview

The islower() function is a member of the <ctype.h> library in C. This function determines if a given character is a lowercase letter from 'a' to 'z'. 

Key Points: 

- The function is available in the <ctype.h> header. 

- It accepts an int as its argument, which typically represents a character. 

- If the character is a lowercase letter, the function returns a non-zero value (true); otherwise, it returns 0 (false).

Source Code Example

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

int main() {
    char ch;

    printf("Enter a character: ");
    scanf("%c", &ch);

    if (islower(ch))
        printf("'%c' is a lowercase letter.\n", ch);
        printf("'%c' is not a lowercase letter.\n", ch);

    return 0;


Enter a character: a
'a' is a lowercase letter.


1. We start by including the necessary header files: stdio.h for input/output functions and ctype.h for the islower() function.

2. In the main() function, we declare a character variable ch.

3. We then prompt the user to input a character.

4. The islower() function checks whether the given character is a lowercase letter.

5. Depending on the result, an appropriate message is printed to the console.