Выдает ошибку в строке с exp найдите ошибку

#include <iostream>
#include <cmath>

using namespace std;

int main()
{
int N = 25;
double Xn = 0.1, Xk = 1, P, Y, x, S, K, h = 0.09, PI = 3.141592653589793238463;
x = Xn;
while (x <= Xk)
{
P=1;
S=P;
for(int i = 0; i <= 25; i++)
{
K = 1;
if (K==0)
P = ((cos(K*(PI/4.0)))/1) * pow(x, K);
else
K *= i;
P= P * (cos((K+1)*(PI/4.0))*x)/((K+1)*cos(K*(PI/4.0)));
S+=P;
cout<<"i = "<<i<<" P = "<<P<<" x = "<<x<<endl;
}

cout<<"S = "<<S<<" Y = "<< pow(exp, x*cos(PI/4.0))*cos(x*sin(PI/4.0))<<"\n\n";
x += h;
S = 0;
K = 1;
}

return 0;
}