Need advice on how to fix

Ok so i am building a beginners program, to have a user input the center of a circle and then a point and find the radius, diameter, area, and circumference. I am suppose to use predefined functions and value returning functions. I put the error of what the compiler said on the line it had a problem with using comments please help if you can.

Code:

#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

double radius(double x, double y, double w, double z);
double diameter(double x);
double circumference(double x);
double area(double x);
const double p = 3.1416;

int main()
{
	double orgin1, orgin2, pt1, pt2, radius, diameter, circumference;
	
	cout << setprecision(2) << fixed << showpoint;
	
	cout << "Please input the origin of your circle" << endl;
	cin >> orgin1 >> orgin2;
	cout << "Please input a point on the circle" << endl;
	cin >> pt1 >> pt2;
	cout << "Your origin is: " << "(" << orgin1 << "," << orgin2 << ")" << endl;
	cout << "Your point is: " << "(" << pt1 << "," << pt2 << ")" << endl;
	cout << "The radius of your circle is: " 
		 << radius(pt1, orgin1, pt2, orgin2) << endl;// term doesn't evaluate 4arguements
	cout << "The diameter of your circle is: " << diameter(radius) << endl;// term
	cout << "The circumference of your circle is: "      // doesn't evaluate 1 arguement
		 << circumference(diameter) << endl; // term doesn't evaluate 1 argument
	cout << "The area of your circle is: " << area(radius) << endl;

	return 0;
}

double radius(double x, double y, double w, double z)
{
	double radius, sum;

	x = pow(x-y,2);
	w = pow(w-z,2);
    sum = x + w;
	radius = sqrt(sum);

	return radius;
}
double diameter(double x)
{
	double diameter;
	diameter = 2 * x;

	return diameter;
}
double circumference(double x)
{
	double cicumference;
	circumference = p * x;

	return circumference; // cannot convert from double to double
}
double area(double x)
{
	double area;
	x = pow(radius, 2); // none of the 7 overloads can convert parameter 1 from
	area = p * x;       // type double

	return area;
}

The problem is your variables have the same names as your functions.

some of the variables are kind-of unnecessary too, although there'd be nothing wrong with them if they had different names

eg,

Code:

double circumference(double d) { return pi*d; }

Also, you may find that your implementation already has "pi" defined as a constant somewhere.