积分：变步长梯形法

#include <stdio.h>
#include <math.h>
#include <iomanip>
#define e 2.7182818
double f(double x)
{
    return pow(e,-x*x);
}
double Calc(double a,double b,double esp)
{
    int done(0);
    int n=1;
    double h,Tn,T2n,k,temp,x;
    h=b-a;
    Tn=h*(f(a)+f(b))/2.0;
    while(!done){
     temp = 0;
     for(k=0;k<n;k++){
      x=a+(k+0.5)*h;
      temp+=f(x);
     }
     T2n=(Tn+h*temp)/2.0;
     if(fabs(T2n-Tn)<esp) done=1;
     else{
      Tn=T2n;
      n=n*2;
      h=h/2;
     }
    }
    return T2n;
}
int main()
{
    printf("%.50lf\n",Calc(-10000,10000,1e-50));
    return 0;
}