Max-heap implementation

Question

Following code for max-heap implementation

#include<iostream>
#include<math.h>
using namespace std;
#define  maxn 1000
int x[maxn];

int parent(int i){
    return int(i/2);

}
int left(int i){
    return 2*i;

}
int right(int i){
    return 2*i+1;

}
void  max_heap(int x[],int i,int size){
    int largest;
    int l=left(i);
    int r=right(i);

    if (l<=size &&  x[l]>x[i]){
        largest=l;
    }
    else
    {
        largest=i;
    }
    if (r<=size && x[r]>x[largest]){
    largest=r;
    }
    if (largest!=i)  { int s=x[i];x[i]=x[largest];x[largest]=s;}
    max_heap(x,largest,size);
}




int main(){

 x[1]=16;
 x[2]=4;
 x[3]=10;
 x[4]=14;
 x[5]=7;
 x[6]=9;
 x[7]=3;
 x[8]=2;
 x[9]=8;
 x[10]=1;
  int size=10;
  max_heap(x,2,size);
   for (int i=1;i<=10;i++)
       cout<<x[i]<<"  ";






    return 0;
}

When I run it, it writes such kind of warning:

1>c:\users\datuashvili\documents\visual studio 2010\projects\heap_property\heap_property\heap_property.cpp(36): warning C4717: 'max_heap' : recursive on all control paths, function will cause runtime stack overflow

Please tell me what is wrong?

Answer 1

The message tells you exactly what's wrong. You haven't implemented any checks to stop the recursion. One smart compiler.

Answer 2

max_heap function doesn't have base case, ie, a return statement. You are just recursively calling the function but never saying when to break another successive call to the max_heap .

Also, in your example you are just calling the function with out satisfying any condition. Usually recursion is done or not done when a case is satisfied.

Answer 3

please tell me what is wrong?

Another problem that I see is that the size of your array x is 10. But the indices that you are using to set values are 1-10.

Answer 4

Put

max_heap(x,largest,size);

inside last check, like this:

if (largest!=i)  
{ 
    int s=x[i];
    x[i]=x[largest];
    x[largest]=s;
    max_heap(x,largest,size);
}

and you're done!

There are many other problems with your code, but to answer your specific question, above change would do!