Max Heap,MIn heap,sort,check max heap or not

#include<bits/stdc++.h>
using namespace std;

int length = 1 ,c = 1;

class Heap
{
public:
    Build_MaxHeap(int arr[])
    {
        int n = length;
        for(int i=n/2;i>=1;i--)
            Max_heapify(arr,i,n);
    }

    Max_heapify(int arr[],int i,int n)
    {
        int leftchild = 2*i;
        int rightchild = 2*i+1;
        int largest;

        if(leftchild<=n && arr[leftchild]>arr[i])
            largest = leftchild;
        else
            largest = i;

        if(rightchild <=n && arr[rightchild]>arr[largest])
            largest = rightchild;

        if(largest != i)
        {
            swap(arr[largest],arr[i]);
            Max_heapify(arr,largest,n);

        }

    }

    Build_MinHeap(int arr[])
    {
        int n = length;
        for(int i=n/2;i>=1;i--)
            Min_heapify(arr,i,n);
    }

    Min_heapify(int arr[],int i,int n)
    {
        int leftchild = 2*i;
        int rightchild = 2*i+1;
        int smaller;

        if(leftchild<=n && arr[leftchild]<arr[i])
            smaller = leftchild;
        else
            smaller = i;

        if(rightchild <=n && arr[rightchild]<arr[smaller])
            smaller = rightchild;

        if(smaller != i)
        {
            swap(arr[smaller],arr[i]);
            Min_heapify(arr,smaller,n);

        }

    }

    Heap_Sort(int arr[],int n)
    {
        Build_MaxHeap(arr);      ///For Sorting First Built Max Heap
        for(int i = 0;i<n;i++)
        {

            swap(arr[1],arr[n-i]);  /// Swap 1st and last element of Max heap since 1st element is the MAX element
            Max_heapify(arr,1,n-i-1);  /// call Max_heapify without last element and again 1st element will be the MAX element
        }
    }


    void check(int arr[],int i,int n)
    {
        int l = 2*i;
        int r = 2*i+1;

       if(i>=1)
       {
            if((l<=n && arr[l]>arr[i])||(r<=n && arr[r]>arr[i]))
            {
              c = 0;
            }
            else
            {
                check(arr,i-1,n);
            }
       }

    }




};




int main()
{
    Heap obj;
    freopen("input.txt","r",stdin);
    int arr[100];
    while(cin)
    {
        cin>>arr[length++];
    }

    length -= 2;

    for(int i = 1;i<= length;i++)
        cout<<arr[i]<<" ";
    cout<<endl<<endl;


    obj.Build_MaxHeap(arr);
    cout<<"Max Heap:"<<endl;
    for(int i = 1;i<= length;i++)
        cout<<arr[i]<<" ";
    cout<<endl<<endl;

    cout<<"Min Heap:"<<endl;
    obj.Build_MinHeap(arr);
    for(int i = 1;i<= length;i++)
        cout<<arr[i]<<" ";
    cout<<endl<<endl;

    cout<<"After Sorting:"<<endl;
    obj.Heap_Sort(arr,length);
    for(int i = 1;i<= length;i++)
        cout<<arr[i]<<" ";
    cout<<endl<<endl;

    obj.check(arr,length/2,length);
    if(c)
        cout<<"MAX HEAP"<<endl<<endl;
    else
        cout<<"Not MAX HEAP"<<endl<<endl;

    return 0;
}