Harvard CS50 Substitution

substitution.c

// substitution.c

// Implement a program that does a substitution cipher with a user supplied key

// Sample Usage

// $ ./substitution qwerTyuIopasDfghjKlzXcVbnm
// Text to encrypt: Wayne is the BEST programmer in the WORLD!
// plaintext:Wayne is the BEST programmer in the WORLD!
// ciphertext:Vqnft ol zit WTLZ hkgukqddtk of zit VGKSR!

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

string cipherKey;

void printCipher(string s, string cipherKeyValue);

bool isAlphaOnly(string s);
bool hasDuplicateCharacter(string s);
bool isCorrectLength(string s);

int main(int argc, string argv[])
{
    if (argc == 2)
    {
        cipherKey = argv[1];

        // A valid cipherKey is 26 alpha characters, no duplicate characters, no numbers or special characters
        if (!isCorrectLength(cipherKey))
        {
            printf("Invalid cipherKey. Must be 26 characters. Substitution cipherKey must include 26 alpha characters only and must not contain any duplicates.");
            return 1;
        }
        if (!isAlphaOnly(cipherKey))
        {
            printf("Invalid cipherKey. Number found. Substitution cipherKey must include 26 alpha characters only and must not contain any duplicates.");
            return 1;
        }
        if (hasDuplicateCharacter(cipherKey))
        {
            printf("Invalid cipherKey. Duplicate character found. Substitution cipherKey must include 26 alpha characters only and must not contain any duplicates.");
            return 1;
        }
    }
    else
    {
        // no cipher cipherKey provided
        printf("You must supply a substitution cipherKey\n");
        return 1;
    }

    string userText = get_string("Text to encrypt: ");

    fputs("plaintext:", stdout);
    puts(userText);
    printCipher(userText, cipherKey);
    printf("\n");

    return 0;

}

// Print out new value after substitution

void printCipher(string s, string cipherKeyValue)
{
    fputs("ciphertext:", stdout);
    char alphabet[] = "abcdefghijklmnopqrstuvwxyz";

    for (int i = 0, length = strlen(s); i < length; i++)
    {
        int valueIndex;

        // check if upper or lower case A..Z
        if ((s[i] >= 65 && s[i] <= 90) || (s[i] >= 97 && s[i] <= 122))
        {
            if ((s[i] >= 65 && s[i] <= 90))
            {
                valueIndex = s[i];
                putchar(toupper(cipherKeyValue[valueIndex-65]));
            }
            else
            {
                valueIndex = s[i];
                putchar(tolower(cipherKeyValue[valueIndex-97]));
            }
        }
        else
        {
            // if not A..Z output the given character
            putchar(s[i]);
        }
    }
    return;
}

// if string is exactly 26 characters in length return true

bool isCorrectLength(string s)
{
    if (strlen(s) == 26)
    {
        return true;
    }
    else
    {
        return false;
    }
}

// if string is only a..z or A..Z return true

bool isAlphaOnly(string s)
{
    bool result = false;

    for (int i = 0, length = strlen(s); i < length; i++)
    {
        if (isalpha(s[i]))
        {
            result = true;
        }
        else
        {
            result = false;
            break;
        }
    }
    return result;
}

// check for duplicates in string

bool hasDuplicateCharacter(string s)
{

    int count = 0;

    for (int i = 0, length = strlen(s); i < length; i++)
    {
        for (int j = 0; j < length; j++)
        {
            if (s[i] == s[j])
            {
                count++;
            }
        }

        // if count is over 1 we found a duplicate, exit
        if (count > 1)
        {
            return true;
        }
        else
        {
            count = 0;
        }
    }
    return false;

}