Getting a Processid from a Findwindow Handle - C++

I was trying to get the process ID of 'Calculator' on C++ using this code.

#define _WIN32_WINNT 0x0501
#include <windows.h>
#include <iostream>
using namespace std;

int main(){
    int wait;
    //Handle - Window name
    HWND windowHandle = FindWindowA(NULL, "Calculator");

    //Getting  ProcessID
    DWORD processID;
    GetWindowThreadProcessId(windowHandle, &processID);

    if(processID){
        cout << "Process ID is: " << processID << endl;
        cin >> wait;
    } else {
        cout << "Unable to find the process id !" << endl;
        cin >> wait;
    }
    return 0;
}

Okay, so i know what you are thinking, that I'm using GetWindowThreadProcessId(), how do I expect to get the actual processID, well I researched a bit and that was all I found.

I want to validate that the window is open by checking the handle from FindWindow using an IF , then if available get it's processID.

Thanks!

THE PROBLEM IS NOW SOLVED

What I was doing is that to check if it's getting the processID I would cout << processID << endl; which is wrong and here is why. The whole line of code GetWindowThreadProcessId(windowHandle, &processID); is what grabs the processID, so to cout the ProcessID we need to store the whole function / line of code in a DWORD. So what I did is edited this line GetWindowThreadProcessId(windowHandle, &processID);

to this:

DWORD actualProcID = GetWindowThreadProcessId(windowHandle, &processID);

Biggest of them all the problem was in the if condition. Here is how it should like (it works):

DWORD processID;
DWORD actualProcId = GetWindowThreadProcessId(windowHandle, &processID);

if(actualProcId){ //We test the DWORD we declared.
    cout << "Process ID is: " << processID << endl; // If true, we cout the process id
    cin >> wait;
} else {
    cout << "Unable to find the process id !" << endl;
    cin >> wait;
}

Thank you for your time!