Introduction to Algorithms Heap Priority Queues

void maxheap(int i)
{
    int left=i*2,right=i*2+1;
    if(a[left]>a[i]&&left<len) big=left;
    else big=i;
    if(a[right]>a[i]&&right<len) big=right;
    swap(big,i);
    maxheap(big);
}
int max_extract()
{
    if(len<1) {cout<<"error"<<endl;
    return;
    }
    int max=a[1];
    a [1] = a [len];
    maxheap(1);
    len--;
    return max;
    
}
void increase_heap(int key,int i)
{
    if(key<a[i])
    {
        cout<<"error"<<endl;
        return;
    }
    a[i]=key;
    while(i>1&&a[i/2]<a[i])
    {
        swap(a[i],a[i/2]);
        i=i/2;
    }
}
void insert_heap(int key)
{
    a [++ len] = INF;
    increase_heap(key,len);
}