caesar.c

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

int main(int argc, string argv[])
{
    //CHeck to see if the correct number of arguments have been entered.
    if (argc != 2)
    {
        printf("Please enter the correct number of arguments\n");
        return 1;
    }
    //Convert argument from string to int
    int key = atoi(argv[1]);
    //Get user input for plaintext
    printf("plaintext: ");
    string plaintext = get_string();
    if (plaintext != NULL)
    {
        printf("ciphertext: ");
        //Iterate through the string and convert each letter
        for (int i = 0, n = strlen(plaintext); i < n; i++)
        {
            //Check for lowercase
            if (islower(plaintext[i]))
            {
                printf("%c", ((((plaintext[i] - 97) + key) % 26) + 97));
            }
            //check for uppercase
            else if(isupper(plaintext[i]))
            {
                printf("%c", ((((plaintext[i] - 65) + key) % 26) + 65));
            }
            //Print non-alpha characters as they are
            else
            {
                printf("%c", plaintext[i]);
            }
        }
    }
    //Print new line to end the deciphered text.
    printf("\n");
    //Exit the program
    return 0;
}