How to use isalpha function

isalpha is a C language function used to determine whether a character is a letter. It is usually used to check whether a character is a letter, including uppercase and lowercase letters.

In C language, the isalpha function is used as follows:

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

The isalpha function accepts an integer parameter c, which can be a character or EOF. The isalpha function returns a nonzero value (usually 1) if c is a letter (uppercase or lowercase), otherwise it returns 0.

For example, the following code demonstrates how to use the isalpha function to check whether a character is a letter:

#include <stdio.h>
#include <ctype.h>
int main() {
    char ch = 'A';
    
    if (isalpha(ch)) {
        printf("%c is a letter\n", ch);
    } else {
        printf("%c is not a letter\n", ch);
    }
    
    return 0;
}

In this example, the isalpha function will check whether the character in the variable ch is a letter, If so, print A is a letter, otherwise print A is not a letter.

It should be noted that the isalpha function needs to include the header file before using it, because the function is declared in this header file.

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