Vigenere fails check50 test encrypts "BaRFoo" as "CaQGon" using "BaZ" error

Question

Vigenere fails check50 test encrypts "BaRFoo" as "CaQGon" using "BaZ" error, my program output is "caQGoh".
I don't know what's the problem but i guess that this problem apears when there are different letter cases(lowercase and uppercase)plus the variance is about 6 shifts.
P.s : I am kind of new to programing and I am trying my best to use function.

Thanks for help :D

//this is my code
#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>


string getChars(string plaintext, string keyword)
{
int txtlen = strlen(plaintext);
int letter;
int j = 0;
for(int i = 0; i < txtlen; i++) 
{
    letter = plaintext[i];

   // check if it's a letter 
    if (isalpha(letter)) 
    {
    // encrypt if letter
        encryptChar(letter, keyword, j);
        j++;
    } 
    // if not just print it
    else 
    {
        printf("%c", letter);
    } 
}

printf("\n");
return 0;
}

char encryptChar(int letter, string keyword, int j)
{
int indexStart;
if (isupper(letter)) 
{
    indexStart = 65;
}

else 
{
    indexStart = 97;
}

char encrypted;
int keyLen = strlen(keyword);
//I guess down here is my problem.
int LtrNum = 0;
if (isupper(letter))
{
    LtrNum = keyword[j % keyLen] - 'A';
}
else if (islower(letter))
{
    LtrNum = keyword[j % keyLen] - 'a';
}
LtrNum = (((letter - indexStart) + LtrNum) % 26);
encrypted = LtrNum + indexStart;

printf("%c", encrypted);

return 0;
}
int main(int argc, string argv[])
{
string keyword = argv[1];
string plaintext = GetString();

// pass the text and the keyword to encrypt  
getChars(plaintext, keyword);

return 0;
}`

Answer 1

I had that error too. I found that change50 is happy if you make the rotation char the same case as the plaintext to be encrypted. (At this point, the plaintext is 'o' and the rotation char is 'Z'-- change it to 'z'. Otherwise you're liable to end up in very strange places.)