CS50 Problem Set 2 (Fall 2020) - Caesar

Caesar.c

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

// function declaration
int encrypt(int k);

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

    int extra = 0;
    int callEncrypt;

    // argc command line should only accept one key
    if (argc != 2 || argc > 2)
    {
        printf("Usage: ./caesar key\n");
        return 1;
    }

    // check if onlly digit or there is some other char in command line
    for (int i = 0, n = strlen(argv[1]); i < n; i++)
    {

        // printf("%c", argv[1][i]);
        if (isdigit(argv[1][i]))
        {

        }
        else
        {
            extra++;
        }

    }
    // if there is extra char other than digit throw error message
    if (extra >= 1)
    {
        printf("Usage: ./caesar key\n");
        return 1;
    }
    // else if convert argv command line to integer
    else
    {
        int key = atoi(argv[1]);
        // call encrypt function
        callEncrypt = encrypt(key);
        return 0;

    }



}

int encrypt(int k)
{
    string text;
    int capitalAlphaIndex = 65;
    int lowerAlphaIndex = 97;
    do
    {
        // prompting to get text
        text = get_string("Plaintext: ");
    }
    // do while to not accept empty
    while (text < 0);
    printf("ciphertext: ");
    // for loop for turning string to char
    for (int i = 0, n = strlen(text); i < n; i++)
    {

        if (isupper(text[i]))
        {
            // if upper encrypts charachter by key but also encrypted text char is Upper
            // converts to capital letters alphabet index by deducing 65
            text[i] =  text[i] - capitalAlphaIndex;
            // applying the formula for encrypt
            text[i] = (text[i] + k) % 26;
            // converts to capital letters back to ASCII so it doesn't ciphers to other ascii characters
            // it ciphers only to alphabets
            text[i] =  text[i] + capitalAlphaIndex;
            printf("%c", text[i]);
        }
        else if (islower(text[i]))
        {
            // converts to lower letters alphabet index by deducing 97
            text[i] =  text[i] - lowerAlphaIndex;
            // applying the formula for encrypt
            text[i] = (text[i] + k) % 26;
            // converts to lower letters back to ASCII so it doesn't ciphers to other ascii characters
            // it ciphers only to alphabets
            text[i] =  text[i] + lowerAlphaIndex;
            printf("%c", text[i]);
        }
        else
        {
            // print as it is if non alphabets
            printf("%c", text[i]);
        }

    }

    printf("\n");
    return 0;
}