problem in Constructor

[programmer0]

Hi everyone,,,i write a class of Rational numbers. My constructor with default parameters shows errors,,why??

class Rational{

private: int a,b;
public:
	Rational(int =1,int =2);
};

Rational::Rational(int a1=1,int b1=2)
{
   a=a1;b=b1;
}

It says "redefinition of default parameter"

[AbstractionAnon]

You can't specify default values on your implementation (line 8).