C - CS50 - Vigenere slightly off with "BaZ" and "BaRFoo" which gives output of "CaQGoh"

Question

I'm at my wits end with this pset2 exercise. When I test my code I get a single error:

:( encrypts "BaRFoo" as "CaQGon" using "BaZ" as keyword \ expected output, but not "CaQGoh\n"

Why in the name of all that is holy would my code work for everything else but this one combination? Fuh realz.

Here's what I got:

int y = 0;

// encipher text
for (int i = 0; i < strlen(phrase); i++) {

    // exclude non-alpha && blank space values
    if ((isalpha(phrase[i])) && (phrase[i] != ' ')) {

        // encode uppercase letters
        if (isupper(phrase[i])) {
            int upper = (((phrase[i] - 'A') + (keyword[y] - 'A')) % 26) + 'A';
            printf("%c", upper);
        } 

        // encode lowercase letters
        else if (islower(phrase[i])) {
            int lower = (((phrase[i] - 'a') + (keyword[y] - 'a')) % 26) + 'a';
            printf("%c", lower);
        }

        // increment or reset keyword character index based on length of keyword - 1
        if (y < (strlen(keyword) - 1)) { y++; } else { y = 0; }
    }

    // otherwise, copy existing character, no adjustment
    else {
        printf("%c", phrase[i]);
    }
}

What gives? Learn me! I am an empty vessel, ready to be schooled in the ways of debuggery!

Answer 1

I'd need to see more of your code or spend more time to understand what's going on, but a couple of points:

\n is the return character, are you creating a newline anywhere in your code?

Secondly, check this question: Vigenere fails check50 testencrypts "BaRFoo" as "CaQGon" using "BaZ" error

Answer 2

As it turns out, not only do you want to check pre-encoded string characters for case, you also have to check the encoding key characters for case to ensure that the values line up appropriately. My updated code is:

int y = 0;

// encipher text
for (int i = 0; i < strlen(phrase); i++) {

    // exclude non-alpha && blank space values
    if ((isalpha(phrase[i])) && (phrase[i] != ' ')) {

        // encode uppercase letters & check case of key value
        if (isupper(phrase[i]) && isupper(keyword[y])) {
            int upper = (((phrase[i] - 'A') + (keyword[y] - 'A')) % 26) + 'A';
            printf("%c", upper);
        }

        // encode uppercase letters & check case of key value
        else if (isupper(phrase[i]) && islower(keyword[y])) {
            int upper = (((phrase[i] - 'A') + (keyword[y] - 'a')) % 26) + 'A';
            printf("%c", upper);
        }

        // encode lowercase letters & check case of key value
        else if (islower(phrase[i]) && islower(keyword[y])) {
            int lower = (((phrase[i] - 'a') + (keyword[y] - 'a')) % 26) + 'a';
            printf("%c", lower);
        }

        // encode lowercase letters & check case of key value
        else if (islower(phrase[i]) && isupper(keyword[y])) {
            int lower = (((phrase[i] - 'a') + (keyword[y] - 'A')) % 26) + 'a';
            printf("%c", lower);
        }

        // increment or reset keyword character index based on length of keyword - 1
        if (y < (strlen(keyword) - 1)) { y++; } else { y = 0; }
    }

    // otherwise, copy existing character, no adjustment
    else {
        printf("%c", phrase[i]);
    }
}