#include<iostream.h>
class complex
{
    public:
        complex()
        {
            real=0;imag=0;
        }
        complex(double r)
        {
            real=r;imag=0;
        }
        complex(double r,double i):real(r),imag(i){};
        friend complex operator+(complex &,complex &);
        void display();
    private:
        double real;
        double imag;
};
complex operator+(complex &c1,complex &c2)
{    
    return complex(c1.real+c2.real,c1.imag+c2.imag);
}
void complex::display()
{
    cout<<real<<"+"<<imag<<"i"<<endl;
}
int main()
{
complex c1(2.8,3),c2;
c2=c1+2.5;
c2.display();
return 0;
}
[color=FF0000][size=5]VC6.0的运行环境，这个错误是怎么回事？[/size][/color]