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

In the C language, the function isalpha() from the header file ctype.h can be used to determine if a character is a letter. The prototype of the isalpha() function is as follows:

#include <ctype.h>
int isalpha(int c);

The function isalpha() takes an integer parameter c, and its return value of a non-zero value (true) indicates that the parameter c is a letter, while a return value of 0 (false) indicates that the parameter c is not a letter.

Here is an example code showing how to use the isalpha() function 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;
}

Run the sample code, input a character, and the program will determine if the character is a letter and output the result.