Error getting template classes to work - c++

Question

I am trying to implement a minHeap of my own and i am getting an error related to my templated class
Here is the main.cpp:
#include <iostream>
#include"road.h"
#include"region.h"
#include"minHeap.h"
using namespace std;
int main()
{
// int numCities;
int numOldRoads;
cin >> numOldRoads;
minHeap<int> roadHeap(numOldRoads);
roadHeap.push(1);
roadHeap.push(4);
roadHeap.push(5);
roadHeap.push(2);
roadHeap.push(7);
roadHeap.push(6);
roadHeap.push(3);
roadHeap.push(9);
roadHeap.push(8);
int temp;
for(int i = 0; i<numOldRoads; i++){
temp = roadHeap.top();
roadHeap.pop();
cout << temp;
}
return 0;
}
Here is the header file:
#ifndef MIN_HEAP
#define MIN_HEAP
template<class T>
class minHeap{
public:
minHeap(int);
void push(T);
void pop();
T top();
void doubleHeapCap();
bool isEmpty();
private:
T *heap;
int heapSize;
int capacity;
};
#endif
Here is the implementation of the minHeap (also in the header because it was giving me errors otherwise):
#include"minHeap.h"
template<class T>
minHeap<T>::minHeap(int theCapacity = 10){
if(theCapacity < 1) throw "Capacity must be >=1.";
capacity = theCapacity;
heapSize = 0;
heap = new T[capacity + 1]; //heap [0] is not used
}
template<class T>
void minHeap<T>::push(const T& e){
//inserts e into min heap
if(heapSize == capacity){ //doubles capacity if Heap is too small
minHeap.doubleHeapCap;
capacity *=2;
}
int currentNode == ++heapSize;
while(currentNode != 1 && heap[currentNode/2] > e){
//bubble up node
heap[currentNode] = heap[currentNode/2]; //moves parent down
currentNode /= 2; //moves current node
}
heap[currentNode] = e;
}
template<class T>
void minHeap<T>::pop(){
//Deletes smallest element from heap and restructures heap
if(isEmpty()) throw "Heap is empty. Cannot delete.";
//deelt smallest element
heap[1].~T();
//remove last element from heap
T lastE = heap[heapSize--];
//trick down to restructure heap
int currentNode = 1; //root of heap
int child = 2; // first child of heap
while(child <= heapSize){
//set child to smaller child of currentNode
if(child < heapSize && heap[child] > heap[child+1]) child++;
//can we put lastE in currenNode?
if(lastE >= heap[child]) break; //yes we can
//no we can't, Obama
heap[currentNode] = heap[child]; //move child up
currentNode = child; child *= 2; // move a level down
}
//after you finally find one, place the node in the corrent position
heap[currentNode] = lastE;
}
template<class T>
bool minHeap<T>::isEmpty(){
//says whether or not hear is empty
if(heapSize == 0) return 1;
else return 0;
}
template<class T>
void minHeap<T>::doubleHeapCap(){
int currentcapacity = this->capacity;
int newCapacity = (this->capacity)*2;
minHeap *temp;
T *newHeap;
//create a new heap with twic the size
newHeap = new T[newCapacity + 1];
//copy elements over
for(int i=0; i<=capacity; i++){
newHeap[i] = this->heap[i];
}
//delete the old heap
temp = heap;
heap = newHeap;
newHeap = 0;
delete[] temp;
}
and here is the error:
In instantiation of 'void minHeap<T>::doubleHeapCap() [with T = int]':
required from 'void minHeap<T>::push(const T&) [with T = int]'
required from here
error: cannot convert 'int*' to 'minHeap<int>*' in assignment|
warning: unused variable 'currentcapacity' [-Wunused-variable]|
I pretty much copied the code from my data structures book and modified it (the book shows an implementation for a Max Heap and i am interested in a min heap).
As you can see all i am trying to do with the main right now is print out the ascending list of integers that i try to push to the min heap.
I think i dont fully understand how to implement template class functions...

Answer 1

In your class declaration you have this:
T *heap;
In doubleHeapCap you have this:
minHeap *temp;
// code...
temp = heap;
If T is int then you are trying to assign an int* (heap) to a minHeap<int>* (temp). Basically, make temp into a T*, too, and it should work. Or you could just dispense with temp altogether and write:
std::swap(heap, newHeap);
delete[] newHeap;