caesar

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

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

    //Make sure ther is only one command line argument
    if (argc != 2)
    {
        printf("Try Again\n");
        return 1;
    }

    //Convert user input string to int
    int k = atoi(argv[1]);


    //Make sure command line argument is non negative
    if (k < 0)
    {
        printf("Try Again\n");
        return 1;
    }
    else
    {

        //Get user input string
        string plainText = get_string("plaintext: ");

        //Place to print cipher text
        printf("ciphertext: ");

        for (int i = 0, n = strlen(plainText); i < n; i++)
        {

            //Encrypt lower case
            if islower(plainText[i])
            {
                printf("%c", (((plainText[i] + k) - 97) % 26) + 97);
            }
            //encrypt upper case
            else if isupper(plainText[i])
            {
                printf("%c", (((plainText[i] + k) - 65) % 26) + 65);
            }
            //print anything else
            else
            {
                printf("%c", plainText[i]);
            }
        }

        printf("\n");

        return 0;
    }
}