Question

I have convex hull algorithm:

#include <cstdlib>
#include <iostream>

using namespace std;
typedef int  point;
 void convexhull(point x[],bool onedge ){

       int N=sizeof(x)/sizeof(int);
       int p=0;
       bool used=new bool[N];
        for (int i=1;i<N;i++){
            if (x[i]<x[p])
            p=i;


            }
            int start=p;
            do
            {

                int n=-1;
                int dist=onedge?32756:0;
                 for (int i=0;i<N;i++){
                     //dont go back  to the same point  you come from
                 if (i==p) continue;
                 if (used[i]) continue;

                  //if there is not such N yet,set it to x
                  if (n==-1) n=i;
                  int cross=(x[i]-x[p])*(x[n]-x[p]);
                  //d is distance  from P to x
                  int d=(x[i]-x[p])*(x[i]-x[p]);
                  if (cross<0){
                     n=i;
                     dist=d;
                           }
                           else if (cross==0){
                                //in this case both N and X  are4 in the 
                                //same direction.if onedge is true
                                //pick the closest one,otherwidr  pick farthest one
                                if (onedge && d<dist){

                                           dist=d;
                                           n=i;


                                           }
                                           else if (!onedge && d>dist)}
                                           dist=d;
                                           n=i;

                                           }





                                }



                }



                p=n;
                used[p]=true;
                } while(start!=p);
}
int main(int argc, char *argv[])
{
    system("PAUSE");
    return EXIT_SUCCESS;
}

But when I compile it, it shows me errors like this:

26 G:\convex_hull.cpp invalid types `bool[int]' for array subscript
48 G:\convex_hull.cpp expected primary-expression before '}' token 
67 G:\convex_hull.cpp expected `,' or `;' before '=' token 

Please help me to understand what is wrong. Can’t I use integer subscripts with bool arrays?

Answer 1

Since you’re declaring a dynamically allocated array, you need a pointer:

bool* used=new bool[N];

You also have a bracket the other way around:

if (!onedge && d>dist) }

instead of

if (!onedge && d>dist) {

Btw, next time please take the time to properly indent your code.