What is the usage of “isnumber” in C++?

In C++, there is no direct isnumber function, but you can use the isdigit function to determine if a character is a number.

The isdigit function is a function in the ctype.h header file, with the following prototype:

int isdigit(int c);

The function isdigit is used to determine if the parameter c is a numerical character (‘0’-‘9’). If it is a numerical character, it returns a non-zero value (true), otherwise it returns zero (false).

Here is an example code using the isdigit function to determine if a character is a number:

#include <iostream>
#include <cctype>

int main() {
    char c = '7';
    if (isdigit(c)) {
        std::cout << "字符 " << c << " 是一个数字" << std::endl;
    } else {
        std::cout << "字符 " << c << " 不是一个数字" << std::endl;
    }
    return 0;
}

The output result is:

字符 7 是一个数字