求助expected primary-expression before '=' token 如何解决

哪位高手帮忙看下哪里出问题了．
代码如下：

#include<iostream>
using namespace std;
#define Pi=3.1415926
class CIRCLE{
private:
float mfR;
public:
CIRCLE(float fR);
void OutputArea();
void OutputCircum();
};
int main()
{
CIRCLE a(1.23),b(5.67);
a.OutputArea();
a.OutputCircum();
b.OutputArea();
b.OutputCircum();
system("pause");
return 0;
}
CIRCLE::CIRCLE(float fR)
{
mfR=fR;
}
void CIRCLE::OutputArea()
{
cout<<"The area is :"<<Pi*mfR*mfR<<endl;
}
void CIRCLE::OutputCircum()
{
cout<<"The circumference is :"<<Pi*mfR*2.0<<endl;
}

编译器提示的信息　28 D:\PChomework\圆类.cpp expected primary-expression before '=' token 哪位高手帮忙解决下．谢谢！