单项选择题
有以下程序
#include<iostream>
using namespace std;
class sample
private:
int x;
public:
sample (int
A.
x=a;
friend double square (sample s);
;
double square (sample s)
return s.x*s.x;
int main()
sample s1(20),s2(30);
cout<<square(s2)<<end1;
return 0;
执行结果是A) 20
B.30
C.900
D.400