c++程序运行程序显示都是0.000000%，为什么？？？

// ConsoleApplication3.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<iostream>

int main()
{
using namespace std;
long long WD_population;
cout.setf(ios_base::fixed, ios_base::floatfield);
cout << "Enter the world's population: ";
cin >> WD_population;
cin.get();
long long US_population;
cout << "Enter the population of US: ";
cin >> US_population;
cin.get();
float percent = US_population / WD_population;
cout << "The population of the US is " << percent << " % of the world population.";
cin.get();
return 0;
}

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