Para começar a desenvolver programas, é necessário antes de tudo decidir qual linguagem se deve trabalhar. Uma das mais recomendadas no mercado hoje em dia e a linguagem JAVA. Entretanto iremos apresentar um pequeno exemplo de uma calculadora simples construída através do programa DEV-C++, que pode ser baixado gratuitamente.

#include <windows.h>
#include <stdlib.h>

LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain (HINSTANCE hThisInstance,
 HINSTANCE hPrevInstance,
 LPSTR lpszArgument,
 int nFunsterStil)
{
 HWND hwnd;
 MSG messages;
 WNDCLASSEX wincl;

 wincl.hInstance = hThisInstance;
 wincl.lpszClassName = "WindowsApp";
 wincl.lpfnWndProc = WindowProcedure;
 wincl.style = CS_DBLCLKS;
 wincl.cbSize = sizeof (WNDCLASSEX);

 wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
 wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
 wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
 wincl.lpszMenuName = NULL;
 wincl.cbClsExtra = 0;
 wincl.cbWndExtra = 0;
 wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;

 if (!RegisterClassEx (&wincl))
 return 0;

 hwnd = CreateWindowEx (
 0,
 "WindowsApp",
 "Calculadora © Por Toca Digital",
 WS_OVERLAPPEDWINDOW,
 350,
 250,
 550,
 100,
 HWND_DESKTOP,
 NULL,
 hThisInstance,
 NULL
 );

 ShowWindow (hwnd, nFunsterStil);

 while (GetMessage (&messages, NULL, 0, 0))
 {
 TranslateMessage(&messages);
 DispatchMessage(&messages);
 }

 return messages.wParam;
}

#define ID_BUTTONmais 1001
#define ID_BUTTONmenos 1002
#define ID_BUTTONvezes 1003
#define ID_BUTTONdividir 1004
#define ID_BUTTONurl 1005
HINSTANCE g_inst;
HWND EditNum1,EditNum2,EditTotal,ButtonMais,ButtonMenos,ButtonVezes,ButtonDividir,ButtonURL;

void DesenharObjectos(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
 EditNum1 = CreateWindowEx (
 WS_EX_CLIENTEDGE,
 //valor inicial (esquerda): 0
 "EDIT",
 "0",
 WS_VISIBLE|WS_CHILD|WS_BORDER|ES_RIGHT ,
 30, 30, 50, 20,
 hwnd,
 NULL,
 g_inst,
 NULL
 );

 EditNum2 = CreateWindowEx (
 //valor inicial (direita): 0
 WS_EX_CLIENTEDGE,"EDIT", "0",
 WS_VISIBLE|WS_CHILD|WS_BORDER,
 160, 30, 50, 20,
 hwnd, NULL, g_inst, NULL );

 EditTotal = CreateWindowEx (
 WS_EX_CLIENTEDGE,"EDIT", "",
 WS_VISIBLE|WS_CHILD|WS_BORDER,
 220, 30, 50, 20,
 hwnd, NULL, g_inst, NULL );

 ButtonMais = CreateWindowEx (
 0,
 "BUTTON",
 "+",
 WS_VISIBLE|WS_CHILD,
 80, 30, 20, 20,
 hwnd,
 (HMENU)ID_BUTTONmais,
 g_inst,
 NULL
 );

 ButtonMenos = CreateWindowEx (
 0, "BUTTON", "-",
 WS_VISIBLE|WS_CHILD,
 100, 30, 20, 20,
 hwnd, (HMENU)ID_BUTTONmenos, g_inst, NULL);

 ButtonVezes = CreateWindowEx (
 0, "BUTTON", "*",
 WS_VISIBLE|WS_CHILD,
 120, 30, 20, 20,
 hwnd, (HMENU)ID_BUTTONvezes, g_inst, NULL);

 ButtonDividir = CreateWindowEx (
 0, "BUTTON", "/",
 WS_VISIBLE|WS_CHILD,
 140, 30, 20, 20,
 hwnd, (HMENU)ID_BUTTONdividir, g_inst, NULL);

 CreateWindowEx (
 0,
 "STATIC",
 "=",
 WS_VISIBLE|WS_CHILD,
 212, 31, 5, 20,
 hwnd,
 NULL,
 g_inst,
 NULL
 );

 ButtonURL = CreateWindowEx (
 0,
 "BUTTON",
 "www.tocadigital.com.br",
 WS_VISIBLE|WS_CHILD,
 272, 30, 230, 20,
 hwnd,
 (HMENU)ID_BUTTONurl,
 g_inst,
 NULL
 );

 SendMessage((HWND) EditNum1,
 (UINT) WM_SETFONT,
 (WPARAM) GetStockObject(DEFAULT_GUI_FONT),
 (LPARAM) lParam
 );

 SendMessage((HWND) EditNum2,(UINT) WM_SETFONT, (WPARAM) GetStockObject(DEFAULT_GUI_FONT),(LPARAM) lParam);
 SendMessage((HWND) EditTotal,(UINT) WM_SETFONT, (WPARAM) GetStockObject(DEFAULT_GUI_FONT),(LPARAM) lParam);

 SendMessage(
 (HWND) ButtonMais,
 (UINT) WM_SETFONT,
 (WPARAM) GetStockObject(DEFAULT_GUI_FONT),
 (LPARAM) lParam
 );

 SendMessage((HWND) ButtonMenos,(UINT) WM_SETFONT, (WPARAM) GetStockObject(DEFAULT_GUI_FONT),(LPARAM) lParam);
 SendMessage((HWND) ButtonVezes,(UINT) WM_SETFONT, (WPARAM) GetStockObject(DEFAULT_GUI_FONT),(LPARAM) lParam);
 SendMessage((HWND) ButtonDividir,(UINT) WM_SETFONT, (WPARAM) GetStockObject(DEFAULT_GUI_FONT),(LPARAM) lParam);
}
void abreURL(){
char szPath[] = "http://www.tocadigital.com.br";
HINSTANCE hRet = ShellExecute(
HWND_DESKTOP, //Parent window
"open", //Operation to perform
szPath, //Path to program
NULL, //Parameters
NULL, //Default directory
SW_SHOW); //How to open
}

char s_valor1[20] = "0", s_valor2[20] = "0", s_total[20] = "0";
int valor1, valor2, total;

LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
 switch (message)
 {
 case WM_CREATE:
 DesenharObjectos(hwnd,message,wParam,lParam);
 break;
 case WM_COMMAND:

 if ((HIWORD(wParam) == BN_CLICKED))
 {

 SendMessage(
 (HWND) EditNum1,
 (UINT) EM_GETLINE,
 (WPARAM) 1,
 (LPARAM) &s_valor1
 );

 SendMessage((HWND)EditNum2,(UINT)EM_GETLINE,(WPARAM)1,(LPARAM) &s_valor2);

 valor1 = atoi(s_valor1);
 valor2 = atoi(s_valor2);

 switch (LOWORD(wParam))
 {
 case ID_BUTTONmais:
 total = valor1+valor2;
 break;
 case ID_BUTTONmenos:
 total = valor1-valor2;
 break;
 case ID_BUTTONvezes:
 total = valor1*valor2;
 break;
 case ID_BUTTONdividir:
 total = valor1 / valor2;
 break;
 case ID_BUTTONurl:
 abreURL();
 break;
 }

 itoa (total,s_total,10);

 SendMessage(
 (HWND) EditTotal,
 (UINT) WM_SETTEXT,
 (WPARAM) 0,
 (LPARAM) &s_total
 );

 }
 break;
 case WM_DESTROY:
 PostQuitMessage (0);
 break;
 default:
 return DefWindowProc (hwnd, message, wParam, lParam);
 }
 return 0;
}