c语言高手进，关于积分的

给，已经编译运行确认：
#include<conio.h>
#include<stdio.h>
#include<math.h>

#define Pi 3.1415926

double integrate(double (*f)(double),double a,double b)
{
double i=1.0/1000000;
double sum=0,x;
for(x=a;x<=b;)
{
sum+=f(x)*i;
x+=i;
}
return sum;
}

double f(double x)
{
return sin(x);
}

int main()
{
double a=0,b=Pi/2;
printf("%lf\n",integrate(f, a, b));

getch();
return 0;
}

运行结果为：1.000000