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

1. isdigit() Function Overview

The isdigit() function is part of the C++ <cctype> library. This function checks if the passed character is a decimal digit character (0-9).

Signature:

int isdigit(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 = '5'; char ch2 = 'A'; if(isdigit(ch1)) { std::cout << "ch1 is a decimal digit character." << std::endl; } else { std::cout << "ch1 is not a decimal digit character." << std::endl; } if(isdigit(ch2)) { std::cout << "ch2 is a decimal digit character." << std::endl; } else { std::cout << "ch2 is not a decimal digit character." << std::endl; } return 0; } 

Output:

ch1 is a decimal digit character. ch2 is not a decimal digit character. 

3. Explanation

In the given example, the isdigit() function is used to determine whether a character is a decimal digit or not. The character '5' is a decimal digit, so for ch1, the function returns true. However, ch2 which holds the character 'A' isn't a decimal digit, hence for ch2, it returns false.