第五週 項目1-當輸入的三條邊不能構成三角形時 ，輸出:

/*
  當輸入的三條邊不能構成三角形時（即不滿足兩邊之和大於第三邊，
  兩邊之差小於第三邊），輸出爲‘nan"

*/
#include <iostream>
#include <cmath>
using namespace std;

class Triangle
{
public:
        void showMessage();
        Triangle (double x,double y,double z);
        Triangle();
        double  perimeter(void );
        double area(void);

private:
       double  a,b,c;

};
Triangle ::Triangle()
{
    a=1;
    b=1;
    c=1;
}

Triangle::Triangle(double x,double y,double z)
{

    a=x;
    b=y;
    c=z;
}


double Triangle::perimeter(void)
{
     double l;
     l=a+b+c;
     return l;
 }
 double Triangle:: area(void)
 {
     double  p,s;
     p=(a+b+c)/2;
     s=sqrt(p*(p-a)*(p-b)*(p-c));
     return s;
 }
 void Triangle::showMessage()
{
    cout<<"該三角形的三條邊爲:"<<'\t'<<a<<'\t'<<b<<'\t'<<c<<endl;
    cout<<"                                                "<<endl;
    cout<<"該三角形的周長爲:"<<'\t'<<perimeter()<<endl;
    cout<<"                                                "<<endl;
    cout<<"該三角形的面積爲:"<<'\t'<<area();

}
int main()
{
    Triangle  t1;
    t1.showMessage ();
    cout<<"                           " <<endl;
    Triangle t2(3,2,44);
    cout<<"                           "<<endl;
    t2.showMessage ();
    return 0;
}