第一次课堂作业——计算圆的面积

https://github.com/laixiaolian/object-oriented

yuan.h

 #define pi 3.14//全局变量

 double circle(double r);//函数申明

yuan.cpp

#include"yuan.h"

double circle(double r)//函数定义
{
    double area;

    area = pi*r*r;

    return area;
}

circle.cpp

#include"yuan.h"

#include<iostream>

using namespace std;

int main()

{
    double area, r;

    cin >> r;

    area = circle(r);//调用函数

    cout<< area << endl;

    return 0;
}