C++編程求助編寫壹個基於對象的程序：輸入半徑，計算圓的周長和面積並輸出

#define Pi 3.14;

class yuan

{

public:

float length(float);

float area(float);

private:

float r;

};

float yuan::length(float r)

{float len;

len=2*Pi*r;}

float yuan::area(floay r)

{float ar;

ar=Pi*r*r;}

void main()

{

yuan m;

cout<<m.length(10.0)<<m.area(10.0)<<endl;

}