Pset 2 Hail Caesar Won't pass check50 even though it works!

Question

I just finished my code for hail Caesar but for some reason when I don't give it a key, instead of exiting the programme and printing it gives me a segmentation error. Also It fails check 50 saying that I encrypt the text wrong but it works correct except the issue with the no key situation.

Any help would be much appreciated, thanks in advance.

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

int lower(int input);
int upper(int input);

int key;

int main(int argc, string argv[])
{

key = atoi(argv[1]);

if (argc != 2)
{
    printf("./caesar key (the key must be an int)");
    return 1;
}

else

{
    printf("Your Key is:%i\nPlease provide me with the plain text my kind sir!:", key);
    string plain = GetString();

    for (int i = 0, n = strlen(plain); i < n; i++)
    {
        if (isalpha(plain[i]))
        {
            if (isupper(plain[i]))
            {
                printf("%c", upper(plain[i]));
            }
            if (islower(plain[i]))
            {
                printf("%c", lower(plain[i]));
            } 
        }
        else
        {
            printf("%c", plain[i]);
        } 
    }
}
}

int upper(int input)
{
int i = input - 65 + key;
i = i % 26;
int k = i + 65;
return k;
}

int lower(int input)
{
int i = input - 97 + key;
i = i % 26;
int k = i + 97;
return k;
}

Answer 1

When main() is called with no key argument, argc is 1 and argv contains only one element, "./ceasar". The problem occurs in key = atoi(argv[1]); which attempts to read the non-existent second index of argv, causing the error. Try moving key = atoi(argv[1]); below if (argc != 2) {...}, so the program will exit before trying to read a garbage value.