CS50 (cs50x) pset2 Substitution Solution 2022

substitution.c

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

//prototype
string valid_key(string key);
string do_text(string start_text, string key);
void swap(char *a, char *b);
string to_lower(string copy_key);

// main function
int main(int argc, string argv[1])
{
    //check argument comannd string
    if (argc == 2)
    {
        string key = argv[1];
        //get memory to copy key
        string copy_key = malloc(strlen(key) + 1);
        //copy key
        strcpy(copy_key, key);
        //tolower copy key
        copy_key = to_lower(copy_key);
        //sorted key to check with etalon
        string key_sort = valid_key(copy_key);
        string key_etalon = "abcdefghijklmnopqrstuvwxyz";
        //compare sorted key with etalon
        if (strcmp(key_sort, key_etalon) == 0)
        {
            //get text
            string start_text = get_string("plaintext:  ");
            //encryption text
            string finish_text = do_text(start_text, key);
            //print encrypted text
            printf("ciphertext: %s\n", finish_text);
            //free memory
            free(copy_key);
            return 0;
        }
        else
        {
            free(copy_key);
            printf("./substitution key\n");
            return 1;
        }
    }
    else
    {
        printf("./substitution key\n");
        return 1;
    }
}

// produce lower char in copy key
string to_lower(string copy_key)
{
    for (int i = 0; i < strlen(copy_key); i++)
    {
        copy_key[i] = tolower(copy_key[i]);
    }
    return copy_key;
}

// swap char in sort
void swap(char *a, char *b)
{
    char temp = *a;
    *a = *b;
    *b = temp;
}

// sort
string valid_key(char *word)
{
    for (unsigned int i = 0; i < strlen(word) - 1; i++)
    {
        for (unsigned int j = i + 1; j < strlen(word); j++)
        {
            if (word[i] > word[j])
            {
                swap(&word[i], &word[j]); // simply swap the characters
            }
        }
    }
    return word;
}

// use check to our text
string do_text(string start_text, string key)
{
    for (int i = 0; i <= strlen(start_text); i++)
    {
        if ((start_text[i] >= 65) && (start_text[i] <= 90))
        {
            start_text[i] = toupper(key[(start_text[i] - 65)]);
        }
        else if ((start_text[i] >= 97) && (start_text[i] <= 122))
        {
            start_text[i] = tolower(key[(start_text[i] - 97)]);
        }
        else
        {
            start_text[i] = start_text[i];
        }
    }
    return start_text;
}