Vigenere

/*
Author: Justin Wheeler
Date: March 7th, 2016
Purpose: This script will take in a keyword and ask for the user to type in a string once executed.
Purpose: After the user complies the program will shuffle the letters in the typed in string by the
Purpose: values in the passed in keyword.
*/

//------------------------------------------------------------
//Libraries
#include <cs50.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>

//------------------------------------------------------------
//Method Signatures
void killProgram(string _output);
void printCipherLetter(int _arr1[], int _arr2[], int _letter, int _keyIndex, string _keycode);
int checkAlpha(string _value);

//------------------------------------------------------------
//Main
int main(int argc, string argv[])
{
    if(argc == 2)
    {
        //Grab Keycode
        string keycode = argv[1];

        if(checkAlpha(keycode) == 0)
        {
            //Alphabets
            int alphabet1[26] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
                  'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};
            int alphabet2[26] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p',
                  'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};

            //Get String to Encrypt
            string userStr;
            userStr = GetString();

            //KeyCode Variables
            int keyBase = strlen(keycode);
            int keyCeil = strlen(keycode);
            int keyIndex = 0;

            //Cycle Through 'userStr' and Cipher Letters
            for(int i = 0; i < strlen(userStr) + 1; i++)
            {
                if(i == strlen(userStr))
                {
                    printf("\n");
                }

                else
                {
                    if(isalpha(userStr[i]))
                    {
                        keyIndex = keyBase % keyCeil;

                        //Uppercase/Uppercase Condition
                        if(isupper(userStr[i]) && isupper(keycode[keyIndex]))
                        {
                            printCipherLetter(alphabet1, alphabet1, userStr[i], keyIndex, keycode);
                        }

                        //Uppercase/Lowercase Condition
                        else if(isupper(userStr[i]) && islower(keycode[keyIndex]))
                        {
                            printCipherLetter(alphabet1, alphabet2, userStr[i], keyIndex, keycode);
                        }

                        //Lowercase/Uppercase Condition
                        else if (islower(userStr[i]) && isupper(keycode[keyIndex]))
                        {
                            printCipherLetter(alphabet2, alphabet1, userStr[i], keyIndex, keycode);
                        }

                        //Lowercase/Lowercase Condition
                        else
                        {
                            printCipherLetter(alphabet2, alphabet2, userStr[i], keyIndex, keycode);
                        }

                        keyBase++;
                    }

                    //Special Characters Condition
                    else
                    {
                        printf("%c", userStr[i]);
                    }
                }
            }
        }

        else
        {
            killProgram("Provide an Alpha Key!\n");
            return 1;
        }
    }

    else
    {
        killProgram("Useage ./vigenere {string key}!\n");
        return 1;
    }

    return 0;
}

//------------------------------------------------------------
//Methods
void killProgram(string _output)
{
    printf("%s\n", _output);
}

void printCipherLetter(int _arr1[], int _arr2[], int _letter, int _keyIndex, string _keycode)
{
    //Cipher Variables
    int indexLetter = 0;
    int indexKey = 0;
    int cipherLetter = 0;

    //Letter Conversion
    for(int j = 0; j < 26; j++)
    {
        if(_letter == _arr1[j])
        {
            indexLetter = j;
            break;
        }
    }

    //Key Conversion
    for(int k = 0; k < 26; k++)
    {
        if(_keycode[_keyIndex] == _arr2[k])
        {
            indexKey = k;
            break;
        }
    }

    //Cipher Output
    cipherLetter = indexLetter + indexKey;

    while(cipherLetter > 25)
    {
        cipherLetter -= 26;
    }

    printf("%c", _arr1[cipherLetter]);
}

int checkAlpha(string _val)
{
    for(int p = 0, len = strlen(_val); p < len; p++)
    {
        if(isalpha(_val[p]) == 0)
        {
            return 1;
        }
    }

    return 0;
}