Код неправильно работает

#include <iostream> 
#include <math.h> 
#include <iomanip>     
 
using namespace std;
const double PI = 3.14159265;
 
typedef double (*uf)(double, double, int &); 
 
void tabl(double, double, double, double, uf); 
double y(double, double, int &); 
double s(double, double, int &); 
 
int main() 
{ 
cout << setw(8) <<"x"<< setw(15) <<"y(x)"<< setw(10) << "k" << endl;
cout << "  ----------------------------------" << endl;
tabl(0.1,0.9,0.1,0.001,y); 
cout << endl; 
cout << setw(8) <<"x"<< setw(15) <<"s(x)"<< setw(10) << "k" <<endl;
cout << "  ----------------------------------" << endl;
tabl(0.1,0.9,0.1,0.001,s); 
return 0; 
}  
void tabl(double a, double b, double h, double eps, uf fun) 
{ 
 int k=0;  
 double sum; 
 for (double x=a; x<b+h/2; x+=h) 
 { k=0;
   sum=fun(x,eps,k); 
   cout << setw(8) << x << setw(15) << sum << setw(10) << k << endl;} 
}  
double y(double x,double eps, int &k) 
{ 
return (exp(x * cos(PI / 4))) * cos(x * sin(PI / 4));
}  
double s(double x, double eps, int &k) 
{ 
 double a=1,c=1,sum=1; 
 //sum=a=x;
 //c=1;
 k=1;
 while (fabs(a)>eps) 
 {
    c*=k*(k+1);
    a=pow(x,k)*cos(k*PI/4)/c;
    sum += a;
    k++;
}
 return sum; 
}

c*=k;