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

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

    if (argc != 2) {
        printf("Invalid input\n");
        return 1;
    }

    int j = atoi(argv[1]);
    // j is the input to move the letters however many spaces

    //prevents the user from using negative integers
    while (j < 0) {
        printf("Invalid input %i, please supply a positive integer\n", j);
        j = get_int();
    }

    if (j > 26) {
        j %= 26;
    }

    printf("plaintext: ");
    string s = get_string();
    //input from user of string to encrypt

    for (int i = 0; i < strlen(s); i++) {

        //These if statements is for the uppercase case
        if (s[i] <= 'Z' && s[i] >= 'A') {

            s[i] += j;

            //wraps back around to uppercase letters
            if (s[i] > 'Z') {

                s[i] -= 26;

            }
        }

        //these if statements are for the lowercase case
        else if (s[i] <= 'z' && s[i] >= 'a') {

            s[i] += j;

            // wraps back around to lowercase letters
            if (s[i] > 'z') {

                s[i] -= 26;

            }
        }

    }
    printf ("ciphertext: %s\n", s);
    return 0;
}