CS50 Vigenere Getting the correct result but unable to submit

Question

I am getting the correct result from the CS50 Vigenere as long as argc does not equal to 1. When it does, it shows runtime error and therefore I am unable to submit this exercise. Can someone please tell me where did I do wrong?

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

int main(int argc, string argv[])
{
    string key = (argv[1]);
    int keylen = strlen(key);

    //make sure the the key is entered and is 1 word
    if (argc != 2)
    {
        printf("Error. Try Again. \n");
        return 1;
    }


    for (int i = 0, n = strlen(key); i < n; i++)
    {
        if (!isalpha(key[i]))
        {
            printf("Error. Try Again.\n");
            return 1;
        }
    }

    //get plaintext from user
    string text = get_string("Plaintext: ");
    printf("ciphertext: ");

    //create integer for key loop

    for (int i = 0, j = 0, textlen = strlen(text); i < textlen; i++, j++)
    {
        if (isalpha(text[i]))
        {
            //check if each character is lowercase
            if islower(text[i])
            {
                printf("%c", 'a' + ((text[i] - 'a') + (key[i % keylen] - 'a')) % 26);
            }
            else if (isupper(text[i]))
            {
                printf("%c", 'A' + ((text[i] - 'A') + (key[i % keylen] - 'A')) % 26);
            }
        }
        // returns all non-alphabet value
        else
        {
            printf("%c", text[i]);
        }

    }

    printf("\n");
    return 0;

}

Answer 1

When argc == 1, it fails because the code is trying to assign argv[1] to key when argv[1] doesn't exist. In other words, the program is executed without a key parameter.

string key = (argv[1]);

The code needs to check that argc == 2 first, in order to catch that condition.

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