Vigenere (Not complete)

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


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

    // Check to make sure only 1 thing is in the command-line
    if (argc != 2) {

        printf("Please enter in the command-line a string of alphabetical characters to compose your key.\n");
        return 1;

    }

        // Get the plaintext
        printf("plaintext: ");
        string plainText = get_string();

        // Take the key convert to string and make var j which will cycle through the key
        string key = argv[1];
        int j = 0;


        if (plainText != NULL) {

            printf("ciphertext: ");

            // Cycle through the plaintext that the user inputed
            for (int i = 0, n = strlen(plainText); i < n; i++) {

                    // If it's a letter
                    if (isalpha(plainText[i])) {

                        // Length of pText % of the length of the key so once it maxes out the key will reset
                        if (strlen(plainText) % strlen(key) == strlen(key)) {

                        j = 0;

                         }

                        // Lowerase letters first
                        if (islower(plainText[i])) {

                            char lower = ((((plainText[i]) - 97) + key[j]) % 26) + 97;
                            printf("%c", lower);
                            j++;

                        }

                        // Uppercase letters
                        else if (isupper(plainText[i])) {

                            char upper = ((((plainText[i]) - 65) + key[j]) % 26) + 65;
                            printf("%c", upper);
                            j++;

                        // Spaces/punctuation
                        } else {

                            printf("%c", plainText[i]);

                        }
                    }

            }

            // Make things look clean and return 0 to show things are all good
            printf("\n");
            return 0;

        }

}