CS50 - WEEK 2 PSET - SUBSTITUTION

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

int quit(void);
char *hash(string argv, string plaintext, string encodedtext);
int calc_checksum(void);

int main(int argc, string argv[])
{
    int checksum = calc_checksum();
    int hashsum = 0;

    if (argc != 2 || strlen(argv[1]) != 26) // Basic checks for arguments
    {
        return quit();     // Exit case 1 - if argument count mismatch
    }
    else
    {
        for (int i = 0; i < 26; i++)
        {
            if (isalpha(argv[1][i]))
            {
                hashsum += toupper(argv[1][i]); // To save me the hassle i have calculated the hashes in uppercase
            }
            else
            {
                return quit();     // Exit case 2 - if Any number is in the key
            }
        }
        if (hashsum == checksum)
        {
            string plaintext = get_string("plaintext:  ");
            char encodedtext[strlen(plaintext)];

            printf("ciphertext: %s\n", hash(argv[1], plaintext, encodedtext));
        }
        else
        {
            return quit();    // Exit case 3 - if the hashes dont match
        }
    }
}

int quit(void)
{
    printf("Usage ./substitution Key\n");
    return 1;
}

char *hash(string argv, string plaintext, string encodedtext)
{
    char key[26];

    for (int i = 0; i < strlen(plaintext); i++)
    {
        if (isupper(plaintext[i]))
        {
            for (int n = 65, j = 0; n <= 90; j++, n++)
            {
                if (plaintext[i] == n)   // This figures out which alphabet it is
                {
                    encodedtext[i] =
                        toupper(argv[j]); // This figures out what key value to be replaced with
                }
                else
                {
                    continue;
                }
            }
        }
        else if (isdigit(plaintext[i]) || !(isalpha(plaintext[i])))
        {
            encodedtext[i] = plaintext[i];     // no replacement happens

        }
        else
        {
            for (int n = 97, j = 0; n <= 122; j++, n++)
            {

                if (plaintext[i] == n)
                {
                    encodedtext[i] =
                        tolower(argv[j]); // This figures out what key value to be replaced with

                }
                else if(plaintext[i] == ' ') {
                    encodedtext[i] = ' ';      // For not neglecting the space in the user text
                }
                else
                {
                    continue;
                }
            }
        }
    }

    encodedtext[strlen(plaintext)] = '\0';
    return encodedtext;
}

int calc_checksum(void)
{
    int sum = 0;
    for (int i = 65; i < 91; i++)
    {
        sum += i;
    }
    return sum;
}