单项选择题

若有以下程序：# include ＜iostream＞using namespace std;class Base{public: Base ( ) { x=0; } int x;};class Derived1 : virtual public Base{public: Derived1 ( ) { x=10; }}; class Derived2 : virtual public Base{public: Derived2 () { x=20; }};class Derived : public Derived1,protected Derived2{ };int main(){ Derived obj; cout＜＜obj.x＜＜end1; return 0;} 该程序运行后的输出结果是

A．10
B．20
C．30
D．0

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单项选择题

有以下程序：#include ＜iostream＞#include ＜math＞using namespace std;class point{private: double x; double y;public: point(double a, double b { x=a; y=b; friend double distance (point a, point b ; };double distance(point a, point b return sqrt((a. x-b. x )*(a. x -b. x )+ (a. x -b. x)*(a. x-b. x));}int main (){ point p1(1,2); point p2(5,2); cout＜＜distance (p1, p2)＜＜end1; return 0;} 程序运行后的输出结果是

A．1
B．5
C．4
D．6

单项选择题

有如下程序#include ＜iostream＞using namespace std;class base{public: virtual void f1() { cout＜＜ F1Base ; } virtual void f2() { cout＜＜ F2Base ; }};class derive: public base{ void f1() { cout＜＜ F1Derive ; } void f2( int x ) { cout＜＜ F2Derive ; }};int main(){ base obj1, * p; derive obj2; p = & obj2; p -＞ f1(); p -＞ f2(); return 0;} 执行后的输出结果是

A．F1Derive F2Base
B．F1Derive F2Derive
C．F1Base F2Base
D．F1Base F2Derive

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