Rectangle.cpp

#include "Rectangle.h"
#include "iostream"
using namespace std;

void main()
{
  cout<< "Welcome! This will give you information of a given rectangle or square.\nJust follow the instructions and you will see."<<endl;
	double width, height;
	cout << "Enter the width" << endl;
	cin>>width;
	cout<<"Enter the height"<<endl;
	cin>>height;
	Rectangle r(width,height);
	cout << "Area: " << r.getArea()<<endl << "Perimeter: " << r.getPerimeter() 
		 << "\nDiagonal Length: " << r.getDiagonalLength() << "\nIs a square: "
		 << boolalpha << r.isSquare() <<"\n\nPress enter to exit";
	cin.ignore();
	cin.ignore();
}

Rectangle.h

#include <cmath>

class Rectangle
{
public:
  double width, height;
	Rectangle(double, double);
	double getArea();
	double getPerimeter(){return (2* width) + (2*height);};
	double getDiagonalLength(){return sqrt(pow(width,2.0) + pow(height, 2.0));};
	bool isSquare(){return width == height;};
};

Rectangle::Rectangle(double a, double b)
{
	width = a;
	height = b;
}

double Rectangle::getArea()
{
	return width * height;
}