Complex Number In C++

class Complex
{
private:
int a,b;
public:
set_data(int,int);
show_data()
{
std:: cout<<"\na="<<a<<"\n"<<"b="<<b;
}
};

Complex::set_data(int x,int y) 
{
a=x;b=y;
}

main()
{
Complex c1;
c1.set_data(3,4);
c1.show_data();
}
Error: error: 'cout' is not a member of 'std' I tired to slove this error but this is not slove