Exercise 2:
a. variable AA is already defined as a class
b. print(); does not have a type like int, void, etc
c. variable CC is already defined as a class

Exercise 4:
a. Line 1
   Line 3
   Line 4

b. CC:CC(){ u = 0; v = 0; }
c. CC:CC(int _u){ u = _u; v = 0; }
d. CC:CC(int _v, int _u){ u = _u; v = _v; }
d. CC:CC(double _v, int _u){ u = _u; v = _v; }


Exercise 5:
a.int testClass::sum(){...}
  void testClass::print(){...}
  testClass::testClass(){...}
  testClass::testClass(int a, int b){...}

b.
#include <iostream>
using namespace std;
class testClass{
public:
  int sum();
  void print();
  testClass();
  testClass(int a, int b);
private:
  int x;
  int y;
};
int main(){
  int a = 0;
  int b = 0;
  testClass testt;
  int x = testt.sum();
  testt.print();
  cin >> a >> b;
  testClass(a,b);
}
int testClass::sum(){
  return x+y;
}
void testClass::print(){
  cout << x << "\t" << y << endl;
}
testClass::testClass(){
  cout << "Default\n";
}
testClass::testClass(int a, int b){
  cout << a << "\t" << b << endl;
}