#include <math.h>
 #include <stdio.h>
 #define EPS 0.000001
 #define ETA 0.01
 #define sqr(x) (x)*(x)
 
 
 double derx(double(*pf)(double), double x)
 {
   double val;
   val=((*pf)(x+ETA)-(*pf)(x-ETA))/(2*ETA);
   return val;
 }
 
double f(double x)
{
 double val;
 val=exp(-x)*sin(x);
 return val;
}
 
 
double integr(double(*pf)(double),double a,double b, int n)
{
  double pas, som;
  int i;
  pas=fabs((b-a))/n;
  som=0.5*(f(a)+f(b));
  for (i=1;i<n;i++)
    {
      som+=f(a+i*pas);
//      printf("pas %g\n",n);
//      printf("i= %g\n",i);
    }
  return som*pas;
}
 
// double f(double x) {return x*x;}
 
 
void main()
{
  double x,y,a,b;
  int n,j;
  FILE *G;
printf("entrer l'intervalle d'integration\n" );
scanf("%lf %lf",&a,&b);
printf("entrer le nombre de pas\n" );
scanf("%d",&n);
printf("pas %g\n",n);
G=fopen("conv.res","w" );
for(j=1;j<n;j++)
 {
  y=integr(f,a,b,j);
    fprintf(G,"%g    %g\n",j,y);
 }
// printf("l'integrale entre %g et %g vaut  %g\n",a,b,y);
fclose(G);
scanf("%lf",&x);
}

Info :Linking C:\DOCUMENTS AND SETTINGS\SEB\MES DOCUMENTS\TP4\integrer1_3.exe
Error:  Error: Unresolved external '_Fopen' referenced from C:\DOCUMENTS AND SETTINGS\SEB\MES DOCUMENTS\TP4\INTEGRER1_3.OBJ