Hi, I'm doing a school project where I need to make a program to calulate the quadratic equation. Now, I already got that part taken care of with the following code:

#include "stdafx.h"
#include "math.h"
#include "stdlib.h"

#using <mscorlib.dll>

using namespace System;


int _tmain()
{
    String *firstnum,
        *secondnum,
        *thirdnum;

    double num1, num2, num3, answer, root, root2, answer1, answer2, complex, complex2, complex3;

    Console::Write(S"Enter the first number: ");
    firstnum = Console::ReadLine();

    Console::Write(S"Enter the second number: ");
    secondnum = Console::ReadLine();

    Console::Write(S"Enter the third number: ");
    thirdnum = Console::ReadLine();

    num1 = Int32::Parse(firstnum);
    num2 = Int32::Parse(secondnum);
    num3 = Int32::Parse(thirdnum);

    answer = num2*num2 - 4*num1*num3;

    if(answer == 0)
    {
        root = -num2/(2*num1);
        Console::WriteLine(S"\nThe answer is {0}.", root.ToString());
    }

    answer1 = sqrt(answer);

    if(answer > 0)
    {
        root2 = (-num2 + answer1) / (2*num1);
        Console::WriteLine(S"\nThe answer is {0}", root2.ToString());
        root2 = (-num2 - answer1) / (2*num1);
        Console::WriteLine(S"\nThe answer is {0}", root2.ToString());
    }

    answer2 = abs(answer);
    complex = sqrt(answer2);

    if(answer < 0)
    {
        complex2 = -num2 / (2*num1);
        complex3 = complex / (2*num1);

        Console::Write(S"\nThe answer is {0}", complex2.ToString());
        Console::Write(S"+{0}", complex3.ToString());
        Console::WriteLine(S"i");

        Console::Write(S"\nThe answer is {0}", complex2.ToString());
        Console::Write(S"-{0}", complex3.ToString());
        Console::WriteLine(S"i");
    }
    return 0;
}

But now I need to do this same thing by creating a GUI using textboxes and such. Now, I would have 3 textbox where the user would input the 3 numbers(num1, num2, num3), do the calulation, then display the answer into a 4th textbox. My problem is I'm not sure how to declare the textbox to equal to the num1, num2, and num3 that I have already used. I hope my question is understandable because I'm kinda new to this. Thanks in advance