Check string consists of alphabet only

Logic. The function isAllAlpha() visits each character of the string. If any character is not a letter (isalpha() from <ctype.h> fails, e.g. a digit, space or symbol), it returns 0 at once. If the loop finishes, all characters are letters and it returns 1. An empty string is treated as not valid.

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

/* returns 1 if every character is a letter, else 0 */
int isAllAlpha(char s[])
{
    if (s[0] == '\0')
        return 0;
    for (int i = 0; s[i] != '\0'; i++)
        if (!isalpha((unsigned char)s[i]))
            return 0;
    return 1;
}

int main(void)
{
    char str[100];
    printf("Enter a string: ");
    scanf("%99s", str);
    if (isAllAlpha(str))
        printf("\"%s\" consists of alphabets only\n", str);
    else
        printf("\"%s\" does not consist of alphabets only\n", str);
    return 0;
}

Sample run (the digit 2 makes the check fail)

Input: Pulchowk2

Enter a string: "Pulchowk2" does not consist of alphabets only