heapsort-code is not working - c++

Question

The following code is not working for heap sort. It looks ok to me. Can someone help me please? I have followed the pseudo code from CLRS, the sorted numbers are not being updated after the algorithm is traversed.
#include <iostream>
using namespace std;
void max_heapify(int *b, int i,int he_size)
{
int l,r,largest;
l=2*i;
r=(2*i+1);
if (l<=he_size && b[l]>b[i])
largest=l;
else largest=i;
if (r<=he_size && b[r]> b[largest])
largest=r;
if (largest!=i)
{
swap(b[i],b[largest]);
max_heapify(b,largest,he_size);
}
}
void build_max_heap(int *c,int h_size,int strlength)
{
for (int q=(strlength)/2;q==1;--q)
{
max_heapify(c,q,h_size);
}
}
void swap(int a, int b)
{
int c=b;
b=a;
a=c;
}
int main()
{
int length;
int heap_size;
cout<<"Enter the number of numbers to be sorted by heap sort"<<endl;
cin>>length;
int* a=NULL;
a=new int[length-1];
int temp;
cout<<"Enter the numbers"<<endl;
for(int i=0;i<length;i++)
{
cin>>temp;
*(a+i)=temp;
}
cout<<"The given numbers are:"<<endl;
for(int j=0;j<length;j++)
cout<<*(a+j)<<" "<<endl;
heap_size= length;
build_max_heap(a,heap_size,length);
for (int l=length;l==2;--l)
{
swap(a[1],a[length]);
heap_size=heap_size-1;
max_heapify(a,1,heap_size);
}
cout<<"The sorted numbers are:"<<endl;
for(int j=0;j<length;j++)
cout<<*(a+j)<<" "<<endl;
system("pause");
return 0;
}

Answer 1

The number of mistakes in your code is enormous. Sorry to say it.
void swap(int a, int b)
{
int c=b;
b=a;
a=c;
}
does nothing - a and b should be passed by link, not by value:
void swap(int &a, int &b)
{
int c=b;
b=a;
a=c;
}
for (int q=(strlength)/2;q==1;--q) is wrong. You meant for (int q=(strlength)/2;q>1;--q). Your loop is running only when q==1.
a=new int[length-1]; The size of array should be length, not length-1. And even though swap(a[1],a[length]); is wrong, because a[length] is out of array.
Also there are some mistakes in algorithm. I tried to rewrite as less code as possible.
Right code is:
#include <iostream>
using namespace std;
void sift_down(int *a, int start, int end) {
int root = start;
while (root * 2 + 1 <= end) {
int child = root * 2 + 1;
int sw = root;
if (a[sw] < a[child])
sw = child;
if (child + 1 <= end and a[sw] < a[child + 1])
sw = child + 1;
if (sw == root)
return;
else
swap(a[root], a[sw]);
root = sw;
}
}
void max_heapify(int *b, int count) {
int start = (count - 2) / 2;
while (start >= 0) {
sift_down(b, start, count - 1);
--start;
}
}
void swap(int &a, int &b) {
int c = b;
b = a;
a = c;
}
int main() {
int length;
int heap_size;
cout << "Enter the number of numbers to be sorted by heap sort" << endl;
cin >> length;
int *a = new int[length];
cout << "Enter the numbers" << endl;
for (int i = 0; i < length; i++) {
cin >> a[i];
}
cout << "The given numbers are:" << endl;
for (int j = 0; j < length; j++)
cout << a[j] << " ";
cout << endl;
heap_size = length;
max_heapify(a, heap_size);
--heap_size;
while (heap_size) {
swap(a[heap_size], a[0]);
--heap_size;
sift_down(a, 0, heap_size);
}
cout << "The sorted numbers are:" << endl;
for (int j = 0; j < length; j++)
cout << a[j] << " ";
cout << endl;
//system("pause");
return 0;
}