Adding forms to a console application.

void handleConsoleButton()
{
    MessageBox(NULL,"Creating the console","msg - handleConsoleButton", MB_OK);
    FreeConsole();
    RedirectIOToConsole();
    printf("Hello, World!\n");
}

/*  This function is called by the Windows function DispatchMessage()  */
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)                  /* handle the messages */
    {
    case WM_DESTROY:
        PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
        break;

    case WM_COMMAND:
        switch LOWORD(wParam)
        {
        case IDC_BTN1:
            MessageBox(NULL,"text1","msg", MB_OK);
            break;
        case IDC_BTN2:
            MessageBox(NULL,"text2","msg", MB_OK);
            break;
        case IDC_BTN3:
            handleConsoleButton();
            break;
        }

    default:                      /* for messages that we don't deal with */
        return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}

#define MAX_CONSOLE_LINES 500

void RedirectIOToConsole()

{

    int hConHandle;

    long lStdHandle;

    CONSOLE_SCREEN_BUFFER_INFO coninfo;

    FILE *fp;

// allocate a console for this app

    AllocConsole();

// set the screen buffer to be big enough to let us scroll text

    GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE),

                               &coninfo);

    coninfo.dwSize.Y = MAX_CONSOLE_LINES;

    SetConsoleScreenBufferSize(GetStdHandle(STD_OUTPUT_HANDLE),

                               coninfo.dwSize);

// redirect unbuffered STDOUT to the console

    lStdHandle = (long)GetStdHandle(STD_OUTPUT_HANDLE);

    hConHandle = _open_osfhandle(lStdHandle, _O_TEXT);

    fp = _fdopen( hConHandle, "w" );

    *stdout = *fp;

    setvbuf( stdout, NULL, _IONBF, 0 );

// redirect unbuffered STDIN to the console

    lStdHandle = (long)GetStdHandle(STD_INPUT_HANDLE);

    hConHandle = _open_osfhandle(lStdHandle, _O_TEXT);

    fp = _fdopen( hConHandle, "r" );

    *stdin = *fp;

    setvbuf( stdin, NULL, _IONBF, 0 );

// redirect unbuffered STDERR to the console

    lStdHandle = (long)GetStdHandle(STD_ERROR_HANDLE);

    hConHandle = _open_osfhandle(lStdHandle, _O_TEXT);

    fp = _fdopen( hConHandle, "w" );

    *stderr = *fp;

    setvbuf( stderr, NULL, _IONBF, 0 );

// make cout, wcout, cin, wcin, wcerr, cerr, wclog and clog

// point to console as well

    ios::sync_with_stdio();

}

#include <windows.h>
#include <stdio.h>
#include <commctrl.h>

#define IDC_BTN1    10000
#define IDC_BTN2    10001
#define IDC_EDIT1   10002
#define IDC_EDIT2   10003
#define IDC_EDIT3   10004


/*  Declare Windows procedure  */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

/*  Make the class name into a global variable  */
char szClassName[ ] = "CodeBlocksWindowsApp";

int WINAPI WinMain (HINSTANCE hThisInstance,
                    HINSTANCE hPrevInstance,
                    LPSTR lpszArgument,
                    int nCmdShow)
{
    HWND hwnd;               /* This is the handle for our window */
    MSG messages;            /* Here messages to the application are saved */
    WNDCLASSEX wincl;        /* Data structure for the windowclass */

    /* The Window structure */
    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure;      /* This function is called by windows */
    wincl.style = CS_DBLCLKS;                 /* Catch double-clicks */
    wincl.cbSize = sizeof (WNDCLASSEX);

    /* Use default icon and mouse-pointer */
    wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;                 /* No menu */
    wincl.cbClsExtra = 0;                      /* No extra bytes after the window class */
    wincl.cbWndExtra = 0;                      /* structure or the window instance */
    /* Use Windows's default colour as the background of the window */
    wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;

    /* Register the window class, and if it fails quit the program */
    if (!RegisterClassEx (&wincl))
        return 0;

    /* The class is registered, let's create the program*/
    hwnd = CreateWindowEx (0,szClassName,"Code::Blocks Template Windows App",WS_OVERLAPPEDWINDOW,CW_USEDEFAULT,CW_USEDEFAULT,
                           450,125, HWND_DESKTOP, NULL, hThisInstance, NULL);


    CreateWindowEx(0,WC_EDIT, "20.02", WS_CHILD|WS_VISIBLE, 20,20, 75,20, hwnd, (HMENU)IDC_EDIT1, hThisInstance, NULL);
    CreateWindowEx(0,WC_BUTTON, "Plus", WS_CHILD|WS_VISIBLE, 120,20, 75,20, hwnd, (HMENU)IDC_BTN1, hThisInstance, NULL);
    CreateWindowEx(0,WC_BUTTON, "Minus", WS_CHILD|WS_VISIBLE, 120,50, 75,20, hwnd, (HMENU)IDC_BTN2, hThisInstance, NULL);
    CreateWindowEx(0,WC_EDIT, "10", WS_CHILD|WS_VISIBLE, 225,20, 75,20, hwnd, (HMENU)IDC_EDIT2, hThisInstance, NULL);

    CreateWindowEx(0,WC_STATIC, "=", WS_CHILD|WS_VISIBLE, 320,20, 15,20, hwnd, (HMENU)NULL, hThisInstance, NULL);

    CreateWindowEx(0,WC_EDIT, "0", WS_CHILD|WS_VISIBLE|ES_READONLY, 350,20, 55,20, hwnd, (HMENU)IDC_EDIT3, hThisInstance, NULL);


    /* Make the window visible on the screen */
    ShowWindow (hwnd, nCmdShow);

    /* Run the message loop. It will run until GetMessage() returns 0 */
    while (GetMessage (&messages, NULL, 0, 0))
    {
        /* Translate virtual-key messages into character messages */
        TranslateMessage(&messages);
        /* Send message to WindowProcedure */
        DispatchMessage(&messages);
    }

    /* The program return-value is 0 - The value that PostQuitMessage() gave */
    return messages.wParam;
}

// returns true if both inputs are valid, false otherwise.
bool readInputs(HWND hwnd, float *num1, float *num2)
{
    const int bufLen = 256;
    char buffer[bufLen];
    HWND editBox1, editBox2;
    int numInputsConverted=0;

    editBox1 = GetDlgItem(hwnd, IDC_EDIT1);
    editBox2 = GetDlgItem(hwnd, IDC_EDIT2);

    GetWindowText(editBox1, buffer, bufLen-1);
    numInputsConverted = sscanf(buffer, "%f", num1);
    if (numInputsConverted == 0)
        return false;

    GetWindowText(editBox2, buffer, bufLen-1);
    numInputsConverted = sscanf(buffer, "%f", num2);
    if (numInputsConverted == 0)
        return false;

    return true;
}

void handleBtn1(HWND hwnd)
{
    float num1, num2, result;
    bool validInputs;
    const int bufLen = 256;
    char buffer[bufLen];
    HWND editBox3;

    editBox3 = GetDlgItem(hwnd, IDC_EDIT3);

    validInputs = readInputs(hwnd, &num1, &num2);
    if (validInputs)
    {
        result = num1 + num2;
        sprintf(buffer, "%0.2f", result);
        SetWindowText(editBox3, buffer);
    }
    else
        MessageBox(hwnd, "Please enter two valid numbers", "Error", MB_ICONERROR|MB_OK);
}

void handleBtn2(HWND hwnd)
{
    float num1, num2, result;
    bool validInputs;
    const int bufLen = 256;
    char buffer[bufLen];
    HWND editBox3;

    editBox3 = GetDlgItem(hwnd, IDC_EDIT3);

    validInputs = readInputs(hwnd, &num1, &num2);
    if (validInputs)
    {
        result = num1 - num2;
        sprintf(buffer, "%0.2f", result);
        SetWindowText(editBox3, buffer);
    }
    else
        MessageBox(hwnd, "Please enter two valid numbers", "Error", MB_ICONERROR|MB_OK);
}


/*  This function is called by the Windows function DispatchMessage()  */
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)                  /* handle the messages */
    {
    case WM_DESTROY:
        PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
        break;

    case WM_COMMAND:
        switch LOWORD(wParam)
        {
        case IDC_BTN1:
            handleBtn1(hwnd);
            break;
        case IDC_BTN2:
            handleBtn2(hwnd);
            break;

        }

    default:                      /* for messages that we don't deal with */
        return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}</commctrl.h></stdio.h></windows.h>