cmath function implementation with RPN calculator - c++

Question

I am having an issue with implementing cmath functions within an RPN calc.
I am noticing different behaviours of my calls. If I have pow(y,x) in the POW statement I receive 0.5 as my answer from the expression:
2 1 arctan cos pow (correct)..
But then using the same code if I enter:
3 recip 8 pow I receive 0 (incorrect)..
However, If I switch the y and x in the pow() call (pow(x,y)) and enter:
2 1 arctan cos pow I receive 0.9 (incorrect)
and if I enter:
3 recip 8 pow I receive 2 (correct)..
I have tried atan(stack.peek()); but that returns 0 with pow(y,x) and 1 with pow(x,y);
My logic must be wrong somewhere I am just unsure.. Thankyou
stack.cpp
int main(int argc, char *argv[]){
HPStack stack;
string line;
while(getline(cin,line)) {
stringstream ss(line);
string token;
while(ss >> token){
if(isdigit(token[0])){
stack.push(atof(token.data()));
} else if (token == "+"){
double x = stack.pop();
double y = stack.pop();
stack.push(y+x);
} else if (token == "-"){
double x = stack.pop();
double y = stack.pop();
stack.push(y-x);
} else if (token == "/"){
double x = stack.pop();
double y = stack.pop();
stack.push(y/x);
} else if (token == "*"){
double x = stack.pop();
double y = stack.pop();
stack.push(y*x);
} else if (token == "COS"){
stack.push(cos(stack.peek()));
} else if (token == "ARCTAN"){
double x = stack.pop();
double y = stack.pop();
stack.push(atan2(x,y));
else if (token == "RECIP"){
double x = stack.peek();
double y = stack.peek();
double recip = 1/y;
stack.push(recip);
} else if (token == "POW"){
double x = stack.pop();
double y = stack.pop();
double sum = pow(y,x);
double answer = (int)(sum*10.0)/10.0;
stack.push(answer);
}
}
cout << stack.peek() << endl;
}
return 0;
}
HPStack.h
#ifndef HPSTACK_H_
#define HPSTACK_H_
class HPStack {
public:
void push(double value);
double pop();
double peek();
private:
double x=0.0,y=0.0,z=0.0,t=0.0;
};
#endif
HPStack.cpp
#include "HPStack.h"
void HPStack::push(double value){
t = z;
z = y;
y = x;
x = value;
}
double HPStack::pop(){
double out;
out = x;
x = y;
y = z;
z = t;
return out;
}
double HPStack::peek(){
return x;
}