复化求积

/*sinx [0,pi/2] */
#include<stdio.h> 
#include<math.h>
#define PI acos(-1)//圆周率; 

int n;//区间段数; 
double h;//步长; 

double f(double x)
{
    return sin(x);
}
double FT(double a,double b)//复化梯形;
{   
    double ans,x;
    int i;

    for(ans=0,i=1;i<=n-1;i++)
    {
        x=a+i*h;
        ans+=f(x);
    }
    ans=(ans*2+f(a)+f(b))*h/2.0;
    return ans;
}
double FS(double a,double b)//复化辛普森; 
{   
    double ans,x,xk;
    int i;
    x=a;xk=x+h/2;
    ans=4*f(xk);
    for(i=1;i<=n-1;i++)
    {
        x=x+h;
        ans+=2*f(x);
        xk=x+h/2.0;
        ans+=4*f(xk);
    }
    ans+=f(a)+f(b);
    ans=ans*h/6;
    return ans;
}
double FC(double a,double b)//复化柯特斯; 
{
    double ans,x,x1,x2,x3;
    int i;
    x=a;
    x1=x+h/4;
    x2=x+h/2;
    x3=x+3*h/4;
    ans=32*f(x1)+12*f(x2)+32*f(x3);
    for(i=1;i<=n-1;i++)
    {
        x=x+h; ans+=14*f(x);
        x1=x+h/4;
        x2=x+h/2;
        x3=x+3*h/4; 
        ans+=32*f(x1)+12*f(x2)+32*f(x3);
    }
    ans+=7*f(a)+7*f(b);
    ans=ans*h/90.0;
    return ans;
}

int main() 
{
    double a=0,b=PI/2.0;
    double ft,fs,fc;
    printf("输入区间划分数n:");
    scanf("%d",&n);
    h=(b-a)/n;
    ft=FT(a,b);fs=FS(a,b);fc=FC(a,b);
    printf("复化梯形求积=%lf:\n",ft);
    printf("复化辛普森求积=%lf:\n",fs);
    printf("复化科特斯求积=%lf:\n",fc);
    return 0;

}