error - f was not declared in this scope - secant method - c++

Question

I am currently working out irr using algorithms through secant method. I think I am doing it correctly so far? but my main problem is that it keeps saying f is not declared in this scope:
int fx1 =f (x1);
int fx2 =f (x2);.
when i try to declare f as a function it does not allow me to, can anyone help?
#include iostream
#include iomanip
#include cmath
using namespace std;
const int Max_Iter=1000;
const double e=0.001;
double internal_r(double c, double r, int n){
double internal_r = 0.0;
for (n=1; n<=Max_Iter; n++); {
internal_r -= c/pow(1.0+r, n);
}
return internal_r;
}
int Secant(double x1, double x2, double e, double &root) {
int fx1 =f (x1);
int fx2 =f (x2);
if (x1==x2|| f(x2)==f(x1)){
root=0; return 0;
}
double x = x1 - f(x1) - (x2-x1) / (f(x2)-f(x1));
if ( fabs(f(x)) < e){
root = x; return 1;
} else {
if (f(x1)*f(x)<0){
return Secant(x1,x,e,root);
} else {
return Secant (x,x2,e,root);
}
}
}
int main() {
int n = 1;
double x1 = 0.0, x2 = 0.0, x = 0.0, fx1 = 0.0, fx2 = 0.0;
cout << "Secant Method" << endl;
cout <<"Enter first initial approximation: ";
cin >>x1;
cout <<"Enter second initial approximation: ";
cin >>x2;
cout <<"Enter the iteration number: ";
cin >>n;
if (n>=0 && n<=Max_Iter) {
cout << "you have entered an iteration sucessfully\n";
x = x1 - (fx1 * (x2 - x1)) / (fx2 - fx1);
cout <<"\n The root of the equation is "<< x <<endl;
return 0;
}
}