I need to create a Rectangle class and then a findMax function which can compare

Question

I need to create a Rectangle class and then a findMax function which can compare an array of Rectangle objects and then return the max by area and then perimeter. Obviously, the way I have written it isn't working quite as expected. Any suggestions to get this to compile and run correctly.

#include
#include
#include

using namespace std;

template

const Object & findMax( const vector& arr, Comparator isLessThan ) {
    int maxIndex = 0;

    for( int i = 1; i < arr.size( ); ++i )
        if( isLessThan( arr[ maxIndex ], arr[ i ]))
          maxIndex = i;

    return arr[ maxIndex ];
}

class Rectangle {

    double length;
    double width;

public:
    explicit Rectangle(double l = 0.0, double w = 0.0) : length{l}, width{w}
    {}
    double getLength() const
      { return length; }
    double getWidth() const
      { return width; }
    double getPerimeter() const
      { return (2 * length) + (2 * width); }
    double getArea() const
      { return length * width; }
};

class PeriCompare {
public:
    bool operator()(const Rectangle & lhs, const Rectangle & rhs) const
    {
      return lhs.getPerimeter(), rhs.getPerimeter();
    }
};

class AreaCompare {
public:
    bool operator()(const Rectangle & lhs, const Rectangle & rhs) const
    {
      return lhs.getArea(), rhs.getArea();
    }
};

int main()
{
    vector rect = {Rectangle{2,3}, Rectangle{1,5}};

    cout<<"Largest perimeter: "<     cout<<"Largest area: "<

    return 0;
}

Explanation / Answer

#include <iostream>
#include <vector>

using namespace std;

class Rectangle {

   double length;
   double width;

public:
   explicit Rectangle(double l = 0.0, double w = 0.0) : length{ l }, width{ w }
   {}
   double getLength() const
   {
       return length;
   }
   double getWidth() const
   {
       return width;
   }
   double getPerimeter() const
   {
       return (2 * length) + (2 * width);
   }
   double getArea() const
   {
       return length * width;
   }
};

class Comparator{
public:
   virtual bool operator()(const Rectangle & lhs, const Rectangle & rhs) const
   {
       return false;
   }
};

class PeriCompare : public Comparator{
public:
   bool operator()(const Rectangle & lhs, const Rectangle & rhs) const
   {
       return lhs.getPerimeter() < rhs.getPerimeter();
   }
};

class AreaCompare : public Comparator{
public:
   bool operator()(const Rectangle & lhs, const Rectangle & rhs) const
   {
       return lhs.getArea() < rhs.getArea();
   }
};

Rectangle findMax(const vector<Rectangle> &arr, Comparator *isLessThan){
   int maxIndex = 0;
   for (unsigned int i = 1; i < arr.size(); ++i){
       if ((*isLessThan)(arr[maxIndex], arr[i])){
           maxIndex = i;
       }
   }
   return arr[maxIndex];
}

int main()
{
   vector<Rectangle> rect = { Rectangle{ 2, 3 }, Rectangle{ 1, 5 } };
   AreaCompare a;
   cout << "Largest perimeter: " << findMax(rect, &PeriCompare()).getPerimeter() << endl;
   cout << "Largest area: " << findMax(rect, &AreaCompare()).getArea() << endl;
  
   return 0;
}

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