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

int a;
string plaintext;
int i;

int main(int argc, string argv[])
{
    a = strlen(argv[1]);

    if (a != 26 && !isalpha(argv[1]))
    {
        printf("Enter a key with 26 alphabetic characters.\n");
        return 1;
    }
    else
    {
        plaintext = get_string("plaintext: ");
        printf("ciphertext: ");

        for (i = 0; i < strlen(plaintext); i++)
        {
            if (isalpha(plaintext[i]))
            {
                if (islower(plaintext[i]))
                {
                    printf("%c", tolower(argv[1][i]));
                }
                else if (isupper(plaintext[i]))
                {
                    printf("%c", toupper(argv[1][i]));
                }
                else
                {
                    printf("%c", argv[1][i]);
                }
            }
            else
            {
                printf("%c", (char)plaintext[i]);
            }
        }

    }

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