定义：#define PI 3.1415926#define F(x) (x+x)使用：a=2*PI*r; //相当于a=2*3.1415926*r;x=7; y=2; z=F(x)*F(x)+F(y)*F(y); // z=(x+x)*(x+x)+(y+y)*(y+y);
