I'm on pset2 vigenere.c. need help with encryption

Question

I've been struggling with vigenere for months. please help me to figure out my errors and guide me clearly. any help much appreciated.

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

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

string p;

if(argc != 2)   //Check if argc is 2 and returns an error if it's not
{
    printf("Please enter a key!\n");

    return 1;
}

string key = argv[1];   //Setting variable key to argv[1]

int keylen = strlen(key);

int j;

for(j = 0; j < keylen; j++)
{
    if(!isalpha(argv[1][j]))
    {
        printf("Enter an alphabetical key!\n");  //Print error message and exit

        return 1;
    }
}
    p = GetString();

    int ptextlen = strlen(p);

    int encrypt;

    int cipherk;

    int cipherp;

    for(int i = 0; i < ptextlen; i++)
    {
        if(isupper(p[i]) && isupper(key[j]))
        {
            cipherk = key[j] - 'A';

            cipherp = p[i] - 'A';

            encrypt = (cipherk + cipherp)%26 + 'A';

            printf("%c", encrypt);
        }
        else if(islower(p[i]) && islower(key[j]))
        {
            cipherk = key[j] - 'a';

            cipherp = p[i] - 'a';

            encrypt = (cipherk + cipherp)%26 + 'a';

            printf("%c", encrypt);
        }
        else if(islower(p[i]) && isupper(key[j]))
        {
            cipherk = key[j] - 'A';

            cipherp = p[i] - 'a';

            encrypt = (cipherk + cipherp)%26 + 'a';

            printf("%c", encrypt);
        }
        else if(isupper(p[i]) && islower(key[j]))
        {
            cipherk = key[j] - 'a';

            cipherp = p[j] - 'A';

            encrypt = (cipherk + cipherp)%26 + 'A';

            printf("%c", encrypt);
        }
        else
        {
            printf("%c", p[i]);
        }
    }

 printf("\n");

 return 0;
}

Answer 1

Struggling for months? wow. And so close!

Have you examined what the code actually does? Specifically, have you looked at the value of j when it encrypts a letter, and how j is initialized and incremented as the encryption for loop is executed?

If this answers your question, please click on the check mark to accept. Let's keep up on forum maintenance. ;-)