Finding predecessor on a heap structure - c

Question

This is the code i'm working and I have a function prototype to build :
node* pred ( int n,node * root) to find the predecessor
I have succeed with building the heap but here I am stuck.Please any held :D
#include<stdio.h>
#include<stdlib.h>
struct MaxHeap
{
int size;
int* array;
};
PrintArray(int* arr, int size);
struct MaxHeap* BuildMaxHeap(int* array, int size);
void HeapSort(int* array, int size);
void swap(int*a, int*b);
void MaxHeapify(struct MaxHeap* maxheap,int index);
int main()
{
int arr[] = {12, 11, 13, 5, 6, 7};
int size = (sizeof(arr))/(sizeof(arr[0]));
printf("\nGiven array of elements is :\n");
PrintArray(arr, size);
HeapSort(arr, size);
printf("\nThe sorted Array is :\n");
PrintArray(arr, size);
return 0;
}
PrintArray(int* arr, int size)
{
int i ;
for (i=0; i<size; i++)
printf("%5d", arr[i]);
printf("\n");
}
void swap(int*a, int*b)
{
int t = *a;
*a = *b;
*b = t;
}
void MaxHeapify(struct MaxHeap* maxheap,int index)
{
int largest = index;
int left = (index <<1) + 1;
int right = (index+1) << 1;
if(left < maxheap->size && maxheap->array[left] > maxheap->array[largest])
largest = left;
if(right < maxheap->size && maxheap->array[right] > maxheap->array[largest])
largest = right;
if(largest != index)
{
swap(&maxheap->array[index], &maxheap->array[largest]);
MaxHeapify(maxheap, largest);
}
}
struct MaxHeap* BuildMaxHeap(int* array, int size)
{
int i;
struct MaxHeap* maxheap = (struct MaxHeap*)malloc(sizeof(struct MaxHeap));
maxheap->size = size;
maxheap->array = array;
for(i= (maxheap->size - 2)/2; i>=0; i--)
MaxHeapify(maxheap, i);
return maxheap;
}
void HeapSort(int* array, int size)
{
struct MaxHeap* maxheap = BuildMaxHeap(array, size);
while(maxheap->size >1)
{
swap(&maxheap->array[0], &maxheap->array[maxheap->size-1]);
maxheap->size -= 1;
MaxHeapify(maxheap, 0);
}
}