Check if a character is a number in the C programming language.

To determine if a character is a digit, you can use the isdigit() function in the C language. This function is part of the C standard library and is used to check if a character is a digit. The prototype of the isdigit() function can be found in the ctype.h header file, which must be included in order to use it.

Here is an example code:

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

int main() {
    char ch = '9';

    if (isdigit(ch)) {
        printf("字符 %c 是数字\n", ch);
    } else {
        printf("字符 %c 不是数字\n", ch);
    }

    return 0;
}

In the code above, the isdigit() function is used to determine if the variable ch is a numeric character. If it is a numeric character, it will output “Character ch is a number”; otherwise, it will output “Character ch is not a number”.

You can modify the value of the variable ch as needed to test if different characters are numeric characters.