C++ time

#include <iostream>
#include <time.h>
using namespace std;

int main()
{
    unsigned int st = (unsigned)time(NULL); //start time
    unsigned int ct = (unsigned)time(NULL); //current time
    unsigned int lt = (unsigned)time(NULL); //last time
    int a = 0;
    cout << "Program will close in 10 seconds" << endl;
    cout << st << endl << ct << endl << lt << endl;
    while(ct - st < 10)
    {

        ct = (unsigned)time(NULL); //update current time
        if(lt != ct)
        {
            a++;
            cout << a << " seconds have passed!" << endl;
            lt = ct;
        }
    }
    cout << "Hello world!" << endl;
    return 0;
}