CS50/caesar

caesar.c

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

int only_digits(string text);
int rotate(char c, int n);

int main(int argc, string argv[])
// Make sure program was run with just one command-line argument

    // Make sure every character in argv[1] is a digit

    // Convert argv[1] from a `string` to an `int`

    // Prompt user for plaintext

    // For each character in the plaintext:

        // Rotate the character if it's a letter
{

    if (argc != 2)
    {
        printf("Usage: ./caesar key\n");
        return 1;
    }
    else if (!only_digits(argv[1]))
    {
        printf("Usage: ./caesar key\n");
        return 1;
    }

    int k = atoi(argv[1]);

    string plaintext = get_string("Plaintext: ");

    printf("Ciphertext: ");

    for (int j = 0; plaintext[j]!='\0'; ++j)
    {
        printf("%c", rotate(plaintext[j], k));
    }
    printf("\n");

}

int only_digits(string text)
{

    for (int i = 0; text[i]!='\0'; ++i)
    {
        if (!isdigit(text[i]))
        {
            return 0;
        }

    }
    return 1;

}

int rotate(char c, int n)
{

    if (isalpha(c))
    {
        if (isupper(c))
        {
            char new_c = (c - 65 + n) % 26 + 65;
            return new_c;
        }
        else
        {
            char new_c = (c - 97 + n) % 26 + 97;
            return new_c;
        }
    }
    else
    {
        return c;
    }

}