Takes user input and encrypts it with a key.

/**
 * caesar.c
 *
 * Koren Leslie Cohen
 *
 * Takes user input and encrypts it.
 *
 *  Usage: ./asciimath key
 */

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

// encrypt user's word by number in command line 
int main(int argc, string argv[])
{
    // declare variables
    int key;
    int result;

    // only accept two command line arguments - key, plaintext string
    if (argc != 2)
    {
        printf("You didn't enter a key. Run program and enter key.\n");
        return 1;
    }

    // get the plain text
    string PlainText = GetString();

    // convert the string/second command line argument (number) to integer 
    key = atoi(argv[1]);

    // if key >= 26, use modulo 26 to wrap back to Aa after Za
    if (key >= 26)
    {
        key = (key % 26);
    }

    // encrypt - iterate over characters in string
    // print each one one at a time
    for(int i = 0, length = strlen(PlainText); i < length; i++)
    {
        // test - printf("In calculating %c + %d...\n", PlainText[i], key);

        // encryption
        result = (PlainText[i] + key);

        // wrapping after Z for uppercase letters
        if (isupper(PlainText[i]) && (result > 'Z'))
        {
            result = (result - 26);
        }

        // wrapping after z for lowercase letters
        if (islower(PlainText[i]) && (result > 'z'))
        {
            result = (result - 26);
        }

        // test - printf("The ASCII value of %c is %d.\n\n", result, result);

        // if character is alphabetical, print encrypted result
        if (isalpha(PlainText[i]))
        {
            printf("%c", result);
        }

       // if non-alphabetical character, print as is   
        else
        {
            printf("%c", PlainText[i]);
        }

    }

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

Result:

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Koren Leslie Cohen

Product manager at Facebook. Former senior product manager at Dollar Shave Club in Los Angeles and software engineer at J.Crew / Madewell in New York City. Recovering trial lawyer.

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Latest posts by Koren Leslie Cohen (see all)

• PM Career Story - April 28, 2022
• How to Transition into Product Management - December 26, 2017
• What I’ve Learned in My First Few Months as a Product Manager - October 14, 2015

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