How to determine if a character is a letter in the C language.

The standard library function isalpha() in C can be used to determine if a character is a letter. This function checks if the character is a letter (including uppercase and lowercase) and returns a non-zero value if it is, otherwise it returns 0.

Here is an example code to determine if a character is a letter:

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

int main() {
    char ch;

    printf("请输入一个字符：");
    scanf("%c", &ch);

    if (isalpha(ch)) {
        printf("%c 是一个字母。\n", ch);
    } else {
        printf("%c 不是一个字母。\n", ch);
    }

    return 0;
}

In the above code, first we use the scanf() function to get the user’s input character and then use the isalpha() function to check if the character is a letter. Based on the return value of isalpha(), we output the corresponding result.

Note: To use the isalpha() function, you need to include the header file .