定义一个复数类，要求能执行“＋”和“－”运算，并能按“a＋bi”的格式显示一个复数。测试这个类。

#include <iostream.h>
class complex
{
public:
complex(){real=imag=0;}
complex(double r,double i)
{real=r;imag=i;}
complex operator+(const complex &c);
complex operator-(const complex &c);
friend void print(const complex &c);
private:
double real,imag;
};
inline complex complex :: operator+(const complex &c)
{return complex (real+c.real,imag+c.imag);}
inline complex complex :: operator-(const complex &c)
{return complex (real-c.real,imag-c.imag);};
void print(const complex &c)
{
if(c.imag<0)
cout<<c.real<<c.imag<<'i';
else
cout<<c.real<<'+'<<c.imag<<'i';
}
void main()
{
complex c1(2.0,3.0),c2(4.0,-5.0),c3;
c3=c1+c2;
cout<<"\nc1+c2=";
print(c3);
c3=c1-c2;
cout<<"\nc1-c2=";
print(c3);