c++ - 为什么这个输出是0%？

Question

此程序将计算比率。正确的输出应该是4.50492%，但是我的输出是0%。我怀疑是尺寸问题。但是，double 的大小是 8 个字节，long long 类型也是如此。我的程序有什么问题？谢谢。

#include <iostream>

int main()
{
    using namespace std;
    //cout << "Enter the world's population: ";
    long long world = 6898758899;
    //cin >> world;
    //cout << "Enter the population of US: ";
    long long us = 310783781;
    //cin >> us;

    double ratio = us/world * 100;
    char percentage = '%';
    cout << "The population of the US is " << ratio << percentage << " of the world population." << endl;

    return 0;
}

Answer 1

因为“us”和“world”类型是long long。所以“us/world”是long long。(long)0.0450492 == 0。

正确的拼写是

double ratio = (double)us/(double)world * 100.0;