GK One-Line Question & Answer

What is 'PIMPL' benefit for compilation?

What is the output: class A{int x=0; public: void set(int v){if(v>=0) x=v;} int get()const{return x;}}; A a; a.set(-5); a.set(3); cout<<a.get();

What is the output: class A{int x; public: A():x(42){} int& ref(){return x;}}; A a; cout<<a.ref();

What is 'interface' vs 'implementation' in encapsulation?

What is the output: class A{int x=0,y=0; public: void move(int dx,int dy){x+=dx;y+=dy;} int getX()const{return x;} int getY()const{return y;}}; A a; a.move(3,4); a.move(-1,2); cout<<a.getX()<<a.getY();

What is the output: class A{int x; public: A(int v):x(v){} int getX()const{return x;} A operator+(const A& o)const{return A(x+o.x);}}; A a(3),b(4); cout<<(a+b).getX();

What is the output: class Counter{int n=0; public: void inc(){n++;} void dec(){n (1, 6, 82, 12, 4, 'What is 'const member function' and const object?

What is 'const member function' and const object?

What is the output: class A{mutable int c=0; public: int get()const{return ++c;}}; const A a; cout<<a.get()<<a.get();

What is the output: class A{int x=0; public: void f(A& o){o.x=5;} int get()const{return x;}}; A a,b; a.f(b); cout<<b.get();

What is the output: class A{int x; public: A(int v):x(v){} bool operator==(const A& o)const{return x==o.x;} bool operator!=(const A& o)const{return !(*this==o);}}; A a(3),b(3),c(4); cout<<(a==b)<<(a!=c);

What is the output: class A{int x=0; public: class B{A& a; public: B(A& a):a(a){} void f(){a.x=10;}}; int get()const{return x;}}; A a; A::B b(a); b.f(); cout<<a.get();

What is the output: class A{int x=5; public: A& setX(int v){x=v; return *this;} int getX()const{return x;}}; A a; cout<<a.setX(10).setX(20).getX();

What is the output: class A{static int n; public: A(){n++;} ~A(){n (1, 6, 82, 12, 4, 'What is the output: class A{int x; public: A(int v):x(v){} void print()const{cout<<x;} friend void f(A a){a.x=99; a.print();}}; A a(5); f(a);', 'Friend function modifies copy?', '99', '99', '5', '5', 'Compile error', 'Compile error', 'Undefined', 'Undefined', NULL, 'option_a', 'f(a) passes by value; f modifies its own copy x=99; prints 99. Output: 99.', 0, '2026-05-25', '2026-05-25'), (1, 6, 82, 12, 4, 'What is 'opaque pointer' (pimpl)?

What is the output: class A{int x; public: A(int v):x(v){} void print()const{cout<<x;} friend void f(A a){a.x=99; a.print();}}; A a(5); f(a);

What is 'opaque pointer' (pimpl)?

What is the output: class A{int x=0; public: void set(int v){x=v;} auto get()const{return x;}}; A a; a.set(7); cout<<a.get();

What is the output: class A{int x=0; public: int& operator[](int i){x=i; return x;}}; A a; a[5]; cout<<a[3];

What is 'accessor' pattern?

What is the output: class A{int x; public: A(int v):x(v){} int operator()(int y)const{return x+y;}}; A a(10); cout<<a(5);

What is the output: class A{int x=1,y=2,z=3; public: tuple<int,int,int> getAll()const{return {x,y,z};}}; A a; auto [x,y,z]=a.getAll(); cout<<x<<y<<z;

What is the output: class A{int x=0; public: void f(){x=42;} int get()const{return x;}}; const A a; a.f();

What is the output: class A{int x=0; public: void set(int v){x=v;} int get()const{return x;} void reset(){x=0;}}; A a; a.set(5); a.reset(); cout<<a.get();

What is the output: class A{int x; public: A(int v):x(v){} A(const A& o):x(o.x){} A& operator=(const A& o){x=o.x;return *this;}}; A a(3); A b=a; b=A(7); cout<<a.x<<b.x;

What is the output: class A{int x=5; public: int get()const{return x;} void set(int v){x=v;}}; A *p=new A; p->set(10); cout<<p->get(); delete p;

What is 'class invariant enforcement'?

What is the output: class A{int x=0; public: A& operator<<(int v){x+=v;return *this;} int get()const{return x;}}; A a; a<<1<<2<<3; cout<<a.get();

What is the output: class A{int x=0; public: int get()const{return x;} void set(int v){x=(v>0?v:x);}}; A a; a.set(-1); a.set(5); cout<<a.get();

What is the output: class A{int x; public: A(int v):x(v){} operator string()const{return to_string(x);}}; A a(42); string s=a; cout<<s;

What is the output: class A{vector<int> v; public: void add(int x){v.push_back(x);} int size()const{return v.size();} int at(int i)const{return v.at(i);}}; A a; a.add(1);a.add(2);a.add(3); cout<<a.size()<<a.at(1);

What is the output: class A{int x=0; public: A& operator+=(int v){x+=v;return *this;} operator int()const{return x;}}; A a; a+=5; a+=3; cout<<(int)a;

What is the output: class A{int x=0; public: int get()const{return x;} friend A operator+(A a,const A& b){a.x+=b.x;return a;}}; A a; a.x; int y=0; //can't access x directly, use friend

What is the output: class A{int x=0; public: void f(){x++;} int g()const{return x;}}; A *p=new A[3]; for(int i=0;i<3;i++) p[i].f(); cout<<p[1].g(); delete[]p;

What is the output: class A{public:virtual int f()=0; int g(){return f()*2;}}; class B:public A{public:int f(){return 5;}}; B b; cout<<b.g();

What is the output: template<typename T> T cube(T x){return x*x*x;} cout<<cube(3)<<cube(2.0);

What is the output: class Stack{vector<int>v; public: void push(int x){v.push_back(x);} int top(){return v.back();} int size(){return v.size();}}; Stack s; s.push(1);s.push(2);s.push(3); cout<<s.top()<<s.size();

What is the output: class A{public:virtual void f()=0;}; class B:public A{public:void f()override{cout<<'B';}}; function<void()> fn=[]{B().f();}; fn();

What is the output: auto add=[](int a,int b){return a+b;}; auto mul=[](int a,int b){return a*b;}; auto apply=[](auto f,int a,int b){return f(a,b);}; cout<<apply(add,3,4)<<apply(mul,3,4);

What is the output: class Queue{deque<int>d; public: void enq(int x){d.push_back(x);} int deq(){int x=d.front();d.pop_front();return x;} int size(){return d.size();}}; Queue q; q.enq(1);q.enq(2);q.enq(3); cout<<q.deq()<<q.size();

What is the output: class A{public:virtual double compute(double x)=0;}; class Square:public A{public:double compute(double x)override{return x*x;}}; class Cube:public A{public:double compute(double x)override{return x*x*x;}}; vector<A*> ops={new Square,new Cube}; for(auto p:ops) cout<<p->compute(3)<<' ';