117.求定积分

#include "stdio.h"
#include "math.h"
double fsimpf(x) /*要进行计算的被积函数*/
double x;
{
  double y;
    y=log(1.0+x)/(1.0+x*x);
    return(y);
}
double fsimp(a,b,eps) /*辛普森算法*/
double a,b,eps; /*a为积分下限，b为积分上限，eps是希望达到的精度*/
{
    int n,k;
    double h,t1,t2,s1,s2,ep,p,x;
    n=1; h=b-a;
    t1=h*(fsimpf(a)+fsimpf(b))/2.0;  /*用梯形公式求出一个大概的估值*/
    s1=t1;
    ep=eps+1.0;
    while (ep>=eps)
  {
    /*用梯形法则计算*/
    p=0.0;
    for (k=0;k<=n-1;k++)
    {
      x=a+(k+0.5)*h;
      p=p+fsimpf(x);
    }
    t2=(t1+h*p)/2.0;
    /*用辛普森公式求精*/
    s2=(4.0*t2-t1)/3.0;
    ep=fabs(s2-s1);
    t1=t2; s1=s2; n=n+n; h=h/2.0;
  }
    return(s2);
}
main()
{
  double a,b,eps,t;
        a=0.0; b=1.0; eps=0.0000001;
      clrscr();
  puts("**********************************************************");
  puts("*         This program is to calculat the Value of       *");
  puts("*          a definite integral by Simpson Method.        *");
  puts("**********************************************************");
      t=fsimp(a,b,eps);
  puts("\n----------------------------------------------------------");
  printf(" >> The result of definite integral is : \n");
  printf(" >> SIGMA(0,1)ln(1+x)/(1+x^2)dx = ");
      printf("%e\n",t);
      puts("----------------------------------------------------------");
      printf("\n Press any key to quit...");
  getch();
}