PSET 2 -- vigenere.c -- So close but just one thing wrong, please help!

Question

I've been banging my head against my keyboard for a while now trying to figure out vigenere.c

I've finally got it really close, but I'm failing just one of the checks when uploading.

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

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

    if(argc != 2)
    {
        printf("You entered an inccorect number of arguments: enter one argument\n");
        return 1;
    }

    char* key = argv[1];
    int keylen = strlen(key);

    for(int i = 0 ; i < keylen ; i++)
    {
        if(!isalpha(key[i]))
        {
            printf("Your key can only be letters of the alphabet");
            return 1;
        }
    }

    char* text = GetString();


    for(int i = 0, j = 0, n = strlen(text) ; i<n ; i++, j++)
    {
        if(j >= keylen) //Resets j to 0 if j is greater than or equal to the keylength
        {
            j = 0;
        }

        if(!isalpha(text[i])) //If character is not alphabetical, subtract j by 1
        {
            j -= 1;
        }

        if(isupper(text[i]))
        {
            text[i] = ((((text[i] - 65) + (key[j] - 65)) % 26) + 65);
            printf("%c", text[i]);
        }
        else if(islower(text[i]))
        {
            text[i] = ((((text[i] - 97) + (key[j] - 97)) % 26) + 97);
            printf("%c", text[i]);
        }
        else
        {
            printf("%c", text[i]);
        }
    }
    printf("\n");
    return 0;
}

Here is the error I'm getting:

Why is BaRFoo encrypting to CaQGoh (lowercase "H" as the last character) instead of CaQGon when BaZ is the key????

If anyone could offer any insight, I would be very grateful!

Answer 1

That particular test is designed to check whether the code can handle the cases where the plain text is lower case and the key is upper case or vice versa. It appears that there is nothing in the code to do this. Forget something? ;-)

The code, as written, assumes that the plain text and the key are the same case.

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