My solution to CS50 pset2 - "Hail, Caesar!"

caesar.c

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

/**
 * Caesar.c
 * A program that encrypts messages using Caesar’s cipher. Your program must
 * accept a single command-line argument: a non-negative integer. Let’s call it
 * k for the sake of discussion. If your program is executed without any
 * command-line arguments or with more than one command-line argument, your
 * program should yell at the user and return a value of 1.
 * 
 * */
 
 int main(int argc, string argv[])
 {
    // check for 2 arguments only
    if (argc != 2)
    {
        printf("Nope\n");
        return 1;
    }
    
    // once I check for correct argv put key into an int k
    int k = atoi(argv[1]);

    // check if the integer is non-negative
    if (k < 0)
    {
        printf("Nope\n");
        return 1;
    }
    else
    {
        // prompt user for a code to encrypt
        string code = GetString();
        
        for (int i = 0, n = strlen(code); i < n; i++)
            {
                //check if the letter is uppercase or lowercase then convert
                if islower(code[i])
                    printf("%c", (((code[i] + k) - 97) % 26) + 97);
                else if isupper(code[i])
                    printf("%c", (((code[i] + k) - 65) % 26) + 65);
                //if neither then just print whatever it is
                else
                    printf("%c", code[i]);
            }
            printf("\n");
            return 0;
    }
 }

Steps:

1. Get a single command-line argument "key" from the user that is a non-negative integer.
2. If not a single argument then yell at user.
3. Take the "key" and turn it into an int with atoi since it starts as a string.
4. Prompt user for a code they want to encrypt.
5. Need to loop through the entire code letter by letter.
6. Check if each letter is either lowercase, uppercase or neither.
7. Standardize the ASCII value of the char to 26 then add the key. Then convert back into ASCII so that the code can wrap around properly.
8. If neither a lowercase or uppercase letter then just print whatever the char is. This allows for spaces or special characters like ! or &.
9. Once all of the above is complete print a new line.
10. Return 0.

Notes:

• Checking if the argv[1] was a non-negative integer (don't think I even needed to do this).
• Figuring out how to standardize ASCII to the regular alphabet then converting back took a lot of time.
• This ASCII chart was incredibly useful - http://www.kerryr.net/pioneers/ascii3.htm
• Trying to put argv[1] into a variable before I check if there is even an argv[1] caused a segmentation fault.
• Didn't notice that toupper/tolower already checks if the character is a letter. First I had two more checks to see if the character was a letter or not when that wasn't necessary.
• ctype.h library is very useful - https://cs50.harvard.edu/resources/cppreference.com/stdstring/all.html

What if the user enters an alphabet instead of a number in place of key?

Guys I'm getting this:

:) caesar.c exists.
:) caesar.c compiles.
:( encrypts "a" as "b" using 1 as key
expected "ciphertext: b...", not "ciphertext: b..."
:( encrypts "barfoo" as "yxocll" using 23 as key
expected "ciphertext: yx...", not "ciphertext: yx..."
:( encrypts "BARFOO" as "EDUIRR" using 3 as key
expected "ciphertext: ED...", not "ciphertext: ED..."
:( encrypts "BaRFoo" as "FeVJss" using 4 as key
expected "ciphertext: Fe...", not "ciphertext: Fe..."
:( encrypts "barfoo" as "onesbb" using 65 as key
expected "ciphertext: on...", not "ciphertext: on..."
:( encrypts "world, say hello!" as "iadxp, emk tqxxa!" using 12 as key
expected "ciphertext: ia...", not "ciphertext: ia..."
:) handles lack of argv[1]
:) handles non-numeric key
:) handles too many arguments

but the output match.... Any idea?

idk
i'm also getting thi with similiar code

were u able to do it?