This was just a template keygen I use for solving crackmes on http://crackmes.de/

BasicKeygenExample.cpp

#include <Windows.h>
#include <malloc.h>
#include <tchar.h>
#include <string>
#include <cstring>
#include <memory.h>
#include <cstdlib>

inline LPWSTR char2wchar(const char *str)
{
	wchar_t *wtext = (wchar_t*)malloc(strlen(str));
	mbstowcs(wtext, str, (1 << 16));
	return wtext;
}

// FUnction prototypes
LRESULT CALLBACK WindowProcedure(HWND, UINT, WPARAM, LPARAM);
HBRUSH CreateHexBrush(int hex)
{
	int red = ((hex >> 16) & 0xFF) / 1.0;
	int green = ((hex >> 8) & 0xFF) / 1.0;
	int blue = ((hex) & 0xFF) / 1.0;

	if (red < 256 && green < 256 && blue < 256)
		return CreateSolidBrush(RGB(red, green, blue));

	return NULL;
}

HINSTANCE hInst;
const char szClassName[] = "Keygen Sample";

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

	wincl.hInstance = hInst = hThisInstance;
	wincl.lpszClassName = szClassName;
	wincl.lpfnWndProc = WindowProcedure;
	wincl.style = CS_DBLCLKS | CS_OWNDC | CS_VREDRAW | CS_HREDRAW;
	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 = CreateHexBrush(0xF0F0F0);

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

	hwnd = CreateWindowEx(
		0, // Extended possibilities for variation
		szClassName, // Class name
		"Keygen",    // Window title
		(WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_MINIMIZEBOX),
		CW_USEDEFAULT, // Window decides position
		CW_USEDEFAULT,  // where the window ends up on the screen
		235,  // Width
		135,  // Height
		HWND_DESKTOP, // The window is a child-window of desktop
		NULL, // No Menu
		hThisInstance,
		NULL // No Creation data
		);

	ShowWindow(hwnd, nFunsterStil);

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

	return messages.wParam;
}

// WIndow procedure for handling window drawing and events
LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lparam)
{
	switch (message)
	{
		case WM_CREATE:
			LOGFONT lf;
			HFONT hMyFont;

			memset(&lf, 0, sizeof(LOGFONT));
			lf.lfWeight = FW_NORMAL;
			lf.lfHeight = 15;
			strcpy(lf.lfFaceName, "Arial");
			hMyFont = CreateFontIndirect(&lf);

			CreateWindowEx(WS_EX_CLIENTEDGE, "button", "Generate", WS_VISIBLE | WS_CHILD, 15, 55, 65, 20, hwnd, (HMENU)1, NULL, NULL);
			CreateWindowEx(WS_EX_CLIENTEDGE, "button", "Leave",    WS_VISIBLE | WS_CHILD, 140, 55, 65, 20, hwnd, (HMENU)2, NULL, NULL);
			CreateWindowEx(WS_EX_CLIENTEDGE, "Edit", "",           WS_VISIBLE | WS_CHILD | WS_BORDER | ES_CENTER, 15, 5, 190, 20, hwnd, (HMENU)3, NULL, NULL);
			CreateWindowEx(WS_EX_CLIENTEDGE, "Edit", "Click Generate", WS_VISIBLE | WS_CHILD | WS_BORDER | ES_CENTER | ES_READONLY | ES_UPPERCASE, 15, 25, 190, 20, hwnd, (HMENU)4, NULL, NULL);

			CreateWindow("STATIC", "Created by Justasic", WS_VISIBLE | WS_CHILD | SS_CENTER, 25, 80, 150, 15, hwnd, (HMENU)5, NULL, NULL);

			// Create the control fonts since the windows normal ones suck
			for (int i = 1; i < 6; ++i)
				SendMessage(GetDlgItem(hwnd, i), WM_SETFONT, (WPARAM)hMyFont, 0);

			break;
		case WM_COMMAND:
			if (LOWORD(wParam) == 1)
			{
				HWND output = GetDlgItem(hwnd, 3);
				HWND genbutton = GetDlgItem(hwnd, 4);

				// Gegerate button called, do ur calcs here.
				const char *str = "Sry. No implement.";
				SetWindowText(output, str);
			}

			if (LOWORD(wParam) == 2)
				PostQuitMessage(0);
			break;
		case WM_CTLCOLORSTATIC:
			// Set the colour of the text for our URL
			if ((HWND)lparam == GetDlgItem(hwnd, 5))
			{
				// we're about to draw the static
				// set the text colour in (HDC)lParam
				SetBkMode((HDC)wParam, TRANSPARENT);
				SetTextColor((HDC)wParam, RGB(255, 0, 0));
				return (BOOL)CreateSolidBrush(GetSysColor(COLOR_MENU));
			}
			break;
		case VK_ESCAPE:
		case WM_DESTROY:
			PostQuitMessage(0);
		default:
			return DefWindowProc(hwnd, message, wParam, lparam);
	}
	return 0;
}