Data Structure that points to a struct

Question

I want to build a priority queue from scratch that points to a struct in C++. I know this can easily be done using the STL library by priority_queue <struct_name> pq . However, I am interested to build this on my own using an array. My initial approach was to build a Min heap for integers and eventually modify the code such that the array points to a struct. To give you more context, here is the code I have written until now.

#include<iostream>

#define MAX_SIZE 100
using namespace std;

struct cell{
    int x, y;
    int depth;
    
    // Constructor
    cell(int x, int y, int depth):
        x(x), y(y), depth(depth) {}
    
    
};

class minHeap{
private:
    // Current size of heap
    int size;
    // Max size of heap
    int capacity;
    // Storing elements as an array
    struct cell* heap = new struct cell[MAX_SIZE];
    // Returns the parent index
    int parent(int i){
        return (i-1)/2;
    }
    // Returns left child
    int leftChild(int i){
        return 2*i + 1;
    }
    // returns right child
    int rightChild(int i){
        return 2*i + 2;
    }
public:
    // Constructor
    minHeap(int capacity){
        size = 0;
        this->capacity = capacity;
        
    }
    
    
    void insert(struct cell node){
        if(size == capacity){
            cout<<"Heap is FULL"<<endl;
            return;
        }
        // Increase the amount of elements in the heap
        size++;
        
        // Insert the element at the end of heap
        heap[size-1] = node;
        
        // Maintain heap invariance
        int i = size - 1;
        while(i!=0 && greater(heap[parent(i)], heap[i])){
            struct cell temp = heap[i];
            heap[i] = heap[parent(i)];
            heap[parent(i)] = temp;
            i = parent(i);
        }
    }
    
    void heapify(int i){
        int left = leftChild(i);
        int right = rightChild(i);
        int smallest = i;
        
        // Find the smallest element of the three
        if((left < size) && greater(heap[left], heap[smallest])){
            smallest = left;
        }
        if((right < size) && (greater(heap[right], heap[smallest]))){
            smallest = right;
        }
        // If the smallest is left or right, keep heapifying
        if(smallest != i){
            struct cell temp = heap[i];
            heap[i] = heap[smallest];
            heap[smallest] = temp;
            heapify(smallest);
        }
        
    }
    
    int extractMin(){
        // Check is heap is empty
        if(size == 0){
            cout<<"Heap is empty"<<endl;
            return -1;
        }
        else if(size == 1){
            size--;
            return heap[0].depth;
        }
        else{
            struct cell root = heap[0];
            heap[0] = heap[size-1];
            size--;
            heapify(0);
            
            return root.depth;
        }
    }
    
    void printHeap(){
        int power = 0;
        int value = 0;
        for(int i=0; i<size; i++){
            if(i == value){
                cout<<endl;
                power += 1;
                value += (1<<power);
            }
            cout<<heap[i].depth<<" ";
        }
        cout<<endl;
    }
};

bool greater(struct cell cell1, struct cell cell2){
        if(cell1.depth == cell2.depth){
            if(cell1.x != cell2.depth){
                return (cell1.x < cell2.x);
            }
            else return cell1.y < cell2.y;
        }
        return cell1.depth < cell2.depth;
    }

int main(){
    minHeap m1(15);
    return 0;
}

However, I run into some errors after this implementation. I have listed them below:

Heap.cpp:24:46: error: no matching function for call to 'cell::cell()'
  struct cell* heap = new struct cell[MAX_SIZE];
                                              ^
Heap.cpp:11:2: note: candidate: cell::cell(int, int, int)
  cell(int x, int y, int depth):
  ^~~~
Heap.cpp:11:2: note:   candidate expects 3 arguments, 0 provided
Heap.cpp:6:8: note: candidate: constexpr cell::cell(const cell&)
 struct cell{
        ^~~~
Heap.cpp:6:8: note:   candidate expects 1 argument, 0 provided
Heap.cpp:6:8: note: candidate: constexpr cell::cell(cell&&)
Heap.cpp:6:8: note:   candidate expects 1 argument, 0 provided
Heap.cpp: In member function 'void minHeap::insert(cell)':
Heap.cpp:59:24: error: missing template arguments before '(' token
   while(i!=0 && greater(heap[parent(i)], heap[i])){
                        ^
Heap.cpp: In member function 'void minHeap::heapify(int)':
Heap.cpp:73:30: error: missing template arguments before '(' token
   if((left < size) && greater(heap[left], heap[smallest])){
                              ^
Heap.cpp:76:32: error: missing template arguments before '(' token
   if((right < size) && (greater(heap[right], heap[smallest]))){

I am relatively new to C++ so I'm not sure if I'm giving all of the information necessary. Please let me know if I can provide any additional details.

Answer 1

Because cell has a constructor with arguments but doesn't have a default (no arguments) constructor listed, you get that first error.

You either need to create a default constructor or make the one you have take a default value on its argument.

Fix that and see how many of your other errors disappear.