用蒙特卡洛方法求解圆周率

Question

//蒙特卡洛法求圆周率
#include
#include
#include
#include

using namespace std;

double FindPi(const long n)
{
srand(time(NULL));
long sum = 0;
double x = 0.0, y = 0.0;
for (long i = 0; i < n; i++)
{
x = (double)(rand())/(double)RAND_MAX;
y = (double)(rand())/(double)RAND_MAX;
if (x*x + y*y <= 1)
{
sum++;
}
if (i % 10000 == 0)
{
system("clear");
cout<<"运行了"<<i<<"次运算，完成了总运算的"<<(double)i/(double)n*100.0<<"%"<<endl;
}
}
return 4.0*((double)sum/(double)n);
}

int main()
{
long n = 0;
cout<<"输入模拟次数:";
cin>>n;
if (n <= 0)
{
cout<<"输入错误"<<endl;
exit(1);
}
double pi = FindPi(n);
cout.precision(50);
cout<<"模拟"<<n<<"次，pi = "<<pi<<endl;
return 0;
}

这个代码为什么算出来的总是在3左右，而不是3.14？

Answer 1

选取的样本是不是太小了？改大点看看。