Using a function input to define the length of an array

[frankthetank]

Hi,

I need to create a function that will evaluate a polynomial at a point x, with the inputs of the function being the coefficients of the polynomial, the order n, and a scalar value of x.

I was given an example problem with a third order polynomial, and so when I wrote the code and the function I defined my arrays as P[4], and everything works fine. However, when I try to replace the 4's with a variable (so P[n+1] rather than P[4]), as it is supposed to work with any order polynomial, visual studio gives me errors like "'P' : unknown size" for all of my arrays.

If anyone could shed some light on what's going wrong, it would be greatly appreciated.

Thanks!
Frank

[frankthetank]

Just thought I'd include my main function so it is easier to see what I am talking about.

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

float polyval(int n, float* p, float x);
int main(void)
{
	int n;
	cout << "Enter polynomial order: ";
	cin >> n;
	float P[n+1], x;
	cout << "Enter coefficients: ";
	for (int i=0;i<n+1;i++) cin >> P[i];
	cout << "Enter a value of x: ";
	cin >> x;
	cout << "The polynomial has value p(x)= " << polyval(n,P,x) << endl;
	return 0;
}

[frankthetank]

I figured it out, I had to create the array using "new"