Code

#include "stdafx.h"
#include <stdlib.h>
#include <string>
#include <iostream>
#include <cmath>
using namespace std;

float Height, Width, Area,Radius;
const float pi = 3.14159265359;
char object,Object;
void area_triangle() {
	system("CLS");
	cout<<"What is the height of the triangle?"<<endl;
	cin>>Height;
	cout<<"What is the width of the triangle?"<<endl;
	cin>>Width;
	system("CLS");
	Area = 0.5 * Height * Width;
	cout<<"The Area of the triangle is : "<<Area<<endl;
	system("pause");
	system("CLS");
}

void area_circul(){
	system("CLS");
	cout<<"What is the Radius of the Circul?"<<endl;
	cin>>Radius;
	system("CLS");
	Area = pi * Radius * Radius;
	cout<<"The Area of the Circul is : "<<Area<<endl;
	system("pause");
	system("CLS");
}

void area_rectangular () {
	system("CLS");
	cout<<"What is the height of the Rectangular?"<<endl;
	cin>>Height;
	cout<<"What is the width of the Rectangular?"<<endl;
	cin>>Width;
	system("CLS");
	Area =  Height * Width;
	cout<<"The Area of the Rectangular is : "<<Area<<endl;
	system("pause");
	system("CLS");
}

void main () {
	cout<<"What is the object you want ot calculate the area of?"<<endl;
	cout<<"use 'C' for Circul, 'R' for rectangular, and 'T' for triangle"<<endl;
	cin>>object;
	Object = toupper(object);
	switch (Object){
		case 'C':
			area_circul();
			main();
			break;
		case 'T':
			area_triangle();
			main();
			break;
		case 'R':
			area_rectangular();
			main();
			break;
		default:
			system("CLS");
			cout<<"you haven't choose the right letter, please try again"<<endl<<endl;
			main();
	}
}