计算pi的近似值

#include <stdio.h>

double f1(double x);
double f2(double x, double y);

int main()
{
    int i; 
    double pi = 8.0/3, a = 4.0, b = 3.0;

    for(i = 0; i < 1e7; i++)
    {
        pi *= f2(a, b);
        a = f1(a);
        b = f1(b);
    }
    printf("%.7f\n", pi);
    return 0;
}

double f1(double x)
{
    return x+2;
}

double f2(double x, double y)
{
    return (x*x)/(y*(y+2));
}

3.1415926

#include <stdio.h>

long long fun1(long long x);
double fun2(long long x);

int main()
{
    long long a = 1, i;
    double r = 0;
    for(i = 0; i < 1e7; i++)
    {  
        r += fun2(a);
        a = fun1(a);
    }
    printf("%.7f\n", r*8);
    return 0;
}

long long fun1(long long x)
{
    return x+4;
}

double fun2(long long x)
{
    return 1.0/(x*(x+2));
}

3.1415926