Функция, вычисляющая площадь треугольника по двум сторонам и углу между ними

#include <cmath>
#include <iostream>
#include <stdio.h>
#include<windows.h>
 
 
using namespace std;
 
float area;
float a,b,angle;
 
void result()
{
area = 0.5 * a * b * sinf(angle * (M_PI / 180));
cout << "Area of triangle = " << area;
}
 
 
 
int main( func,  result)
{
  func();
  result();
 
  system("pause");
  return 0;
}
void func()
{
cout << "First side(a) - ";
    cin >> a;
cout << "Second side(b) - ";
    cin >> b;
cout << "Angle between sides of triangle - ";
    cin >> angle;
 
    area = 0.5 * a * b * sinf(angle * (M_PI / 180));
}

void func();

#define _USE_MATH_DEFINES
#include <cmath>
#include <iostream>
using namespace std;
 
void input(double&,double&,double&);
double result(double a,double b,double angle)
{
    return 0.5 * a * b * sin(angle * M_PI / 180.);
}
 
int main()
{
    double area,a,b,angle;
    input(a,b,angle);
    area=result(a,b,angle);
    cout << "Area of triangle = " << area<<endl;
    system("pause");
    return 0;
}
void input(double& a,double& b,double& angle)
{
    cout << "First side(a) - ";
    cin >> a;
    cout << "Second side(b) - ";
    cin >> b;
    cout << "Angle between sides of triangle - ";
    cin >> angle;
 
    //area = 0.5 * a * b * sinf(angle * (M_PI / 180));
}