Pset 2 - Vigenere - segmentation fault

Question

So i wrote my program, but when i start it, i get the segmentation fault, yet when i start it with debug50 it works, i know what is the segmentation fault, but i can't figure out why and where would this segmentation fault happen,

I was thinking that it might happen in line 33 if the condition to reset the key letter doesn't trigger (if i reach the last letter of the key, go back to the first letter), but there are no reasons that it wouldn't

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

// Constants
#define ASCIILOWERCASE 97;
#define ASCIIUPPERCASE 65;
#define ALPHABETICALLENGTH 26;

// Functions prototypes
int charCrypter(char keyChar, char uncryptedChar);
int indexValue(char asciiChar);

int main(int argc, string argv[])
{
    // Exit program if CLI is wrong
    if (argc != 2 || isalpha(argv[1]) == false)
    {
        return 1;
    }

    string userKey = argv[1];
    string userInputText = get_string("Text: ");
    int letter = 0;

    // Main loop of the program
    for (int i = 0, n = strlen(userInputText); i < n; i++)
    {
        if (isalpha(userInputText[i]))
        {
            // Loop the key
            if (letter == strlen(userKey))
            {
                letter = 0;
            }
            printf("%c", charCrypter(userKey[letter], userInputText[i]));
            letter++;
        }
        else
        {
            printf("%c", userInputText[i]);
        }
    }
}

// Encrypt the character
int charCrypter(char keyChar, char uncryptedChar)
{
    // get the index value
    int keyIndex = indexValue(keyChar);
    int userIndex = indexValue(uncryptedChar);

    int alphabeticalValue = (keyIndex + userIndex) % ALPHABETICALLENGTH

    // Cipher the uncrypted char
    if (islower(uncryptedChar))
    {
        return alphabeticalValue + ASCIILOWERCASE;
    }
    return alphabeticalValue + ASCIIUPPERCASE;
}

// Get index value
int indexValue(char asciiChar)
{
    if (islower(asciiChar))
    {
        return asciiChar - ASCIILOWERCASE;
    }
    return asciiChar - ASCIIUPPERCASE;
}

Answer 1

Your segmentation fault is happening at this line:

    // Exit program if CLI is wrong
    if (argc != 2 || isalpha(argv[1]) == false)

You might take a look at the documentation of isalpha. The function isalpha takes a char as its argument. However, you give it a string as argument ...

Hint on how to solve this: Remember that a string is basically a char * or a char[] ...

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Finally, to quote Cliff B:

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