The isalpha check on the keyword works strangely

Question

I've just started the vigenere task, and so far implemented only the starting point - a check, whether the keyword input is alphabetical. It works as intended, when the keyword starts with a non-alphabetical char, in all other cases it looks like the check is not working. What is the problem here?

#include <stdio.h>
#include <stdlib.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>

int main (int argc, string argv[])
{
    if (argc != 2)
    {
        printf("Don't joke with me, cowboy! I said enter the name of the programm AND one keyword ONLY. Try again!");
        return 1;
    }

    string keyword = argv[1];
    for (int i = 0, l = strlen(keyword); i < l; i++)
    {
        if (isalpha(keyword[i]))
        {
        return 0;
        }
        else
        {
            printf("Looks like you've entered an invalid keyword. Remeber, your keyword must contain letter only. Try again!");
        return 1;
        }
    }
    printf("Enter the text you want to cipher: \n");
}

Answer 1

    if (isalpha(keyword[i]))
    {
    return 0;

Ummm.... is there a reason you want to end the program with a return statement when the first char is a letter?

As written, this code is going to end the program as soon as it looks at the first char, either by returning a 1 or a 0. It will never get past the first char, and it definitely won't get past the first pass of the for loop.

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