3.STRUCT

#define _USE_MATH_DEFINES
#include <iostream>
#include <string>
#include <math.h>
#include <cmath>
struct Circle
{
    float r;
}; // Circumference=2*pi*r
//area=pi*r*r
struct Rectangle
{
    float a;
    float b;
};//Circumference =2a +2b;
//area = ab;
struct Triangle
{
    float a;
    float h;
    float b;
    float c;
};// Circumference= L=a+b+c
//area= 1/2*a*h
double Circumference(const Triangle& triangle)
{
    return triangle.a + triangle.b + triangle.c;
}
double area(const Triangle& triangle)
{
    return 0.5* triangle.a * triangle.h;
}
double Circumference(const Rectangle& rectangle)
{
    return (2 * rectangle.a) + (2 * rectangle.b);
}
double area(const Rectangle& rectangle)
{
    return rectangle.a * rectangle.b;
}
Triangle readTriangle()
{
    Triangle h;
    std::cout << "a=";
    std::cin >> h.a;
    std::cout << "h=";
    std::cin >> h.h;
    std::cout << "b=";
    std::cin >> h.b;
    std::cout<<"c=";
    std::cin >> h.c;
    return h;
}
void handleTriangle()
{
    Triangle h = readTriangle();
    std::cout << "Circumference = " << Circumference(h);
    std::cout << std::endl;
    std::cout << "Area=" << area(h);
}
Rectangle readRectangle()
{
    Rectangle r;
    std::cout << "a =";
    std::cin >> r.a;
    std::cout << "b=";
    std::cin >> r.b;
    return r;

}
void handleRectangle()
{
    Rectangle r = readRectangle();
    std::cout << "Circumference: " << Circumference(r);
    std::cout << std::endl;
    std::cout << "Area:" << area(r);
}
double Circumference(const Circle& circrle)
{
    return 2 * M_PI * circrle.r;

}
double area(const Circle& circle)
{
    return M_PI * circle.r * circle.r;
}
Circle readCircle()
{
    Circle c;
    std::cout << "r = ";
    std::cin >> c.r;

    return c;
}
void handleCircle()
{
    Circle c = readCircle();
    std::cout << "Circumference: " << Circumference(c);
    std::cout << std::endl;
    std::cout << "Area: " << area(c);
}
void choose()
{
    int answer;
    std::cout << "[1] Circle" << std::endl;
    std::cout << "[2]rectangle" << std::endl;
    std::cout << "[3]triangle" << std::endl;
    std::cout << "enter:";
    std::cin >> answer;
    switch (answer)
    {
    case 1:
    {
        handleCircle();
        break;
    }
    case 2:
    {
        handleRectangle();
        break;
    }
    case 3:
    {
        handleTriangle();
        break;

    }
    }
}
int main()
{
    choose();
}