浮点数输出很多位小数出现错误

Question

 #include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    char str[1000];
    sprintf(str,"%.100lf",(double)1/250);
    cout<<str;
}

运行这个程序得到的结果是
0.004000000000000000000000000000000中间有一段非零数字
00000000000000000000

Answer 1