Affine Key Finder and Decrypter, C++ (vc++)

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//Microsoft (R) C/C++ Optimizing Compiler Version 19.00.23506 for x64

#include <iostream>
#include <vector>

using std::cout;
using std::cin;
using std::endl;
using std::vector;

/*
    The purpose for this struct is to hold my possible alpha and beta
    values that the program found to fit the conversions. The struct
    is stored into a vector that holds all possible values.
*/
struct AB
{
    int alpha;
    int beta;
};

/*
    My main function that computes all 312 conversions from plaintext
    to ciphertext. Using the plain -> cipher conversion from HW1.6, the
    program will find the possible combinations of alpha and beta values
    from samples of that conversion.
*/
void main()
{
    // I begin by storing all possible values of alpha and beta into two
    // separate arrays. I also initialize my storage containers.
    int alphArray[12] = {1, 3, 5, 7, 9, 11, 15, 17, 19, 21, 23, 25};
    int betaArray[26];
    vector<AB> possibleAB;
    AB temp;
    
    // I use a loop to store the 26 values of beta instead of doing the same
    // process as the alphArray.
    for (int i = 1; i <= 26; i++)
    {
        betaArray[i-1] = i;
    }
    
    // This nested for loop is the main component that finds the possible
    // conversions using two arbitrarily chosen conversions from HW1.6 as
    // a key. In this case, I took the conversions R -> D (ie 17 -> 3) and
    // P -> Z (ie 15 ->25).
    for (int i = 0; i < 12; i++)
    {
        for (int j = 0; j < 26; j++)
        {   
            if ( ((alphArray[i]*17) + betaArray[j]) % 26 == 3 && ((alphArray[i]*15) + betaArray[j]) % 26 == 25)
            {
                temp.alpha = alphArray[i];
                temp.beta = betaArray[j];
                
                possibleAB.push_back(temp);
            }
        }
    }
    
    // Luckily from these two conversions, there was only one outcome. If
    // there had been more, I would have added more conversions from the
    // example to weed out more possibilities.
    
    // This loop is just to see what were the values that were found to
    // satisfy the conversion.
    cout << "Possible combinations: " << possibleAB.size() << endl;
    for (int i = 0; i < possibleAB.size(); i++)
    {
        cout << "My alpha value: " << possibleAB[i].alpha << endl;
        cout << "My beta value: " << possibleAB[i].beta << endl << endl;
    }
    
    if (possibleAB.size() == 1)
    {
        int testD;
        int yDe;
        cin >> testD;
       
    while ( !cin.fail() )
    {
        if (possibleAB[1].alpha == 1)
        {                
            yDe = (1*(testD - possibleAB[1].beta)) % 26;
        }
        else if (possibleAB[1].alpha == 3)
        {                
            yDe = (9*(testD - possibleAB[1].beta)) % 26;
        }
        else if (possibleAB[1].alpha == 5)
        {                
            yDe = (21*(testD - possibleAB[1].beta)) % 26;
        }
        else if (possibleAB[1].alpha == 7)
        {                
            yDe = (15*(testD - possibleAB[1].beta)) % 26;
        }
        else if (possibleAB[1].alpha == 9)
        {                
            yDe = (3*(testD - possibleAB[1].beta)) % 26;
        }
        else if (possibleAB[1].alpha == 11)
        {                
            yDe = (19*(testD - possibleAB[1].beta)) % 26;
        }
              
        if ( testD == 0)
        {
            cout << "The letter: A" << endl;
        }
        else if ( testD == 1)
        {
            cout << "The letter: B" << endl;
        }
        else if (testD == 2)
        {
            cout << "The letter: C" << endl;
        }
        else if (testD == 3)
        {
            cout << "The letter: D" << endl;
        }
        else if (testD == 4)
        {
            cout << "The letter: E" << endl;
        }
        else if (testD == 5)
        {
            cout << "The letter: F" << endl;
        }
        else if (testD == 6)
        {
            cout << "The letter: G" << endl;
        }
        else if (testD == 7)
        {
            cout << "The letter: H" << endl;
        }
        else if (testD == 8)
        {
            cout << "The letter: I" << endl;
        }
        else if (testD == 9)
        {
            cout << "The letter: J" << endl;
        }
        else if (testD == 10)
        {
            cout << "The letter: K" << endl;
        }
        else if (testD == 11)
        {
            cout << "The letter: L" << endl;
        }
        else if (testD == 12)
        {
            cout << "The letter: M" << endl;
        }
        else if (testD == 13)
        {
            cout << "The letter: N" << endl;
        }
        else if (testD == 14)
        {
            cout << "The letter: O" << endl;
        }
        else if (testD == 15)
        {
            cout << "The letter: P" << endl;
        }
        else if (testD == 16)
        {
            cout << "The letter: Q" << endl;
        }
        else if (testD == 17)
        {
            cout << "The letter: R" << endl;
        }
        else if (testD == 18)
        {
            cout << "The letter: S" << endl;
        }
        else if (testD == 19)
        {
            cout << "The letter: T" << endl;
        }
        else if (testD == 20)
        {
            cout << "The letter: U" << endl;
        }
        else if (testD == 21)
        {
            cout << "The letter: V" << endl;
        }
        else if (testD == 22)
        {
            cout << "The letter: W" << endl;
        }
        else if (testD == 23)
        {
            cout << "The letter: X" << endl;
        }
        else if (testD == 24)
        {
            cout << "The letter: Y" << endl;
        }
        else if (testD == 25)
        {
            cout << "The letter: Z" << endl;
        }
        
        cout << "Decrypts to: ";
    
        if ( yDe == 0)
        {
            cout << "A" << endl;
        }
        else if ( yDe == 1)
        {
            cout << "B" << endl;
        }
        else if (yDe == 2)
        {
            cout << "C" << endl;
        }
        else if (yDe == 3)
        {
            cout << "D" << endl;
        }
        else if (yDe == 4)
        {
            cout << "E" << endl;
        }
        else if (yDe == 5)
        {
            cout << "F" << endl;
        }
        else if (yDe == 6)
        {
            cout << "G" << endl;
        }
        else if (yDe == 7)
        {
            cout << "H" << endl;
        }
        else if (yDe == 8)
        {
            cout << "I" << endl;
        }
        else if (yDe == 9)
        {
            cout << "J" << endl;
        }
        else if (yDe == 10)
        {
            cout << "K" << endl;
        }
        else if (yDe == 11)
        {
            cout << "L" << endl;
        }
        else if (yDe == 12)
        {
            cout << "M" << endl;
        }
        else if (yDe == 13)
        {
            cout << "N" << endl;
        }
        else if (yDe == 14)
        {
            cout << "O" << endl;
        }
        else if (yDe == 15)
        {
            cout << "P" << endl;
        }
        else if (yDe == 16)
        {
            cout << "Q" << endl;
        }
        else if (yDe == 17)
        {
            cout << "R" << endl;
        }
        else if (yDe == 18)
        {
            cout << "S" << endl;
        }
        else if (yDe == 19)
        {
            cout << "T" << endl;
        }
        else if (yDe == 20)
        {
            cout << "U" << endl;
        }
        else if (yDe == 21)
        {
            cout << "V" << endl;
        }
        else if (yDe == 22)
        {
            cout << "W" << endl;
        }
        else if (yDe == 23)
        {
            cout << "X" << endl;
        }
        else if (yDe == 24)
        {
            cout << "Y" << endl;
        }
        else if (yDe == 25)
        {
            cout << "Z" << endl;
        }
        
        cin >> testD;
        }
    }
}

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Compilation time: 1,79 sec, absolute running time: 0,21 sec, absolute service time: 2,02 sec