求多个积分函数之和遇到问题了，连接出现错误 undefined  _fftsf symbol  in module，要怎么解决？积分函数可以这样写么？

#include "stdio.h"
  #include "ffts.c"                       
  main()
  { double a,b,eps,t1,t2,sum,fftsf(double);
    a=0.0; b=1.0; eps=0.000001;
    t1=ffts(a,b,eps,fftsf);
    a=1.0; b=2.0; eps=0.000001;
    t2=ffts(a,b,eps,fftsf);
    sum=t1+t2;
    printf("\n");
    printf("sum=%e\n",sum);
    printf("\n");
  return 0;
  }

  #include "math.h"
  double fftsf1(x)
    { double y;
    y=exp(-x*x);
    return(y);
  }
double fftsf2(x)
  double x;
  { double y;
    y=exp(-x*x*x);
    return(y);
  }

定积分啊，写的很清楚。
哪看不明白么？

是这样的，再看看。


#include "math.h"
  double ffts(a,b,eps,f)
  double a,b,eps,(*f)();
  { int n,k;
    double fa,fb,h,t1,p,s,x,t;
    fa=(*f)(a); fb=(*f)(b);
    n=1; h=b-a;
    t1=h*(fa+fb)/2.0;
    p=eps+1.0;
    while (p>=eps)
      { s=0.0;
        for (k=0;k<=n-1;k++)
          { x=a+(k+0.5)*h;
            s=s+(*f)(x);
          }
        t=(t1+h*s)/2.0;
        p=fabs(t1-t);
        t1=t; n=n+n; h=h/2.0;
      }
    return(t);
  }


  #include "stdio.h"
  #include "9ffts.c"
  main()
  {
   double a,b,eps,t1,t2,sum,fftsf(double);
   a=0.0; b=1.0; eps=0.000001;
     t1=ffts(a,b,eps,fftsf);
   a=1.0; b=2.0; eps=0.000001;
     t2=ffts(a,b,eps,fftsf);
     sum=t1+t2;
   printf("\n");
   printf("sum=%e\n",sum);
   printf("\n");
     return 0;
  }

  #include "math.h"
  double fftsf1(x)
   {
  double y;
    y=exp(-x*x);
    return(y);
   }

  double fftsf2(x)
   {
   double y;
   y=exp(-x*x*x);
   return(y);
   }