如下程序声明了一个电话号码类PhoneNumber，重载了流插入运算符＜＜，以便于电话号码的输出。请将程序补充完整。
include＜iostream＞
include＜iomanip＞
include＜string＞
using namespace std;
class PhoneNumber{
public:
void setNumber(string number) {this--＞number = number;}
//重载流插入操作符
friend【 】(ostream &output,const PhoneNumber &num)
{ output＜＜num. number; return output; }
private:
string number;
};
int main() {
PhoneNumber phone;
phone. setNumber("8008100598");
cout＜＜"The phone number is:"＜＜phone＜＜endl;
return 0;
}