C++ Function Parameter Arguments passed by pointer

#include <iostream>
using namespace std;
int main()/*  www.  jav  a  2s . c  om*/
{
   void centimize(double*);    //prototype
   double var = 10.0;          //var has value of 10 inches
   cout << "var = " << var << " inches" << endl;
   centimize(&var);            //change var to centimeters
   cout << "var = " << var << " centimeters" << endl;
   return 0;
}
void centimize(double* ptrd)
{
   *ptrd *= 2.54;              //*ptrd is the same as var
}