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

int main(int argc, string argv[])
{
    //Make sure that there is only 1 correct argument
    if (argc != 2)
    {
        printf("Usage: ./caesar k\n");
        return 1;
    }

    else
    {
        //Once I get the correct argument,k ,change the string into an int
        int k = atoi(argv[1]);

        //Make sure the integer is non-negative
        if (k < 0)
        {
            printf("Usage: ./caesar k , k must be more than 0\n");
            return 1;
        }

        else
        {
            //Prompt user for a code to encrypt
            string s = get_string("plaintext:");
            printf("ciphertext: ");
            for (int i = 0, n = strlen(s) ; i < n ; i++)
            {
                if (isalpha(s[i]))
                {
                    //Encrypt Uppercase letter
                    if (isupper(s[i]))
                    {
                        printf("%c", ((s[i] - 'A' + k) % 26) + 'A');
                    }
                    //Encrypt Lowercase Letter
                    if (islower(s[i]))
                    {
                        printf("%c", ((s[i] - 'a' + k) % 26) + 'a');
                    }
                }
                //Print back the text without changes
                else
                {
                    printf("%c", s[i]);
                }
            }
            //Print a new line
            printf("\n");
            return 0;
        }
    }
}