islower() function in C++

In this guide, you will learn what is islower() function is in C++ programming and how to use it with an example.

1. islower() Function Overview

The islower() function is part of the C++ <cctype> library. It checks if the given character is a lowercase alphabetic letter (a-z).

Signature:

int islower(int ch);

Parameters:

- ch: The character to be checked. Although it's an int, it essentially represents the ASCII value of the character.

2. Source Code Example

#include <iostream>
#include <cctype>

int main() {
    char ch1 = 'g';
    char ch2 = 'M';

    if(islower(ch1)) {
        std::cout << "ch1 is a lowercase alphabetic letter." << std::endl;
    } else {
        std::cout << "ch1 is not a lowercase alphabetic letter." << std::endl;
    }

    if(islower(ch2)) {
        std::cout << "ch2 is a lowercase alphabetic letter." << std::endl;
    } else {
        std::cout << "ch2 is not a lowercase alphabetic letter." << std::endl;
    }

    return 0;
}

Output:

ch1 is a lowercase alphabetic letter.
ch2 is not a lowercase alphabetic letter.

3. Explanation

In this example, the islower() function is used to determine whether a character is a lowercase letter. 

The character 'g' is lowercase, so for ch1, the function returns true. 

On the other hand, ch2 contains the uppercase character 'M', hence for ch2, it returns false.