C++代码：面积计算

包括圆形、矩形、三角形。

#include <iostream>
#include<cmath>
const double PI=3.14;
using namespace std;

double area(double r)
{
   double s;
   s= PI*r*r;
   return s;
}

double area(double a, double b)
{
    double s;
    s=a*b;
    return s;
}

double area(double a, double b, double c)
{
    double p,s;
    p=(a+b+c)/2;
    s=sqrt(p*(p-a)*(p-b)*(p-c));
    return s;
}

int main()
{
    double r,a,b,c;
    cin>>r;
    cout<<"圆的面积为："<<area(r)<<endl;
    cin>>a>>b;
    cout<<"矩形的面积为："<<area(a,b)<<endl;
    cin>>a>>b>>c;
    cout<<"三角形的面积为："<<area(a,b,c)<<endl;
    return 0;
}