Programming In C++
Spring 2000
CSCI 2200 CRN: 90349

Test #2 Topics

Sample Questions

(Sample answers are at the end of this page)

Expect questions related to the sample code we've gone over in class! Below are a few sample questions based on code very similar to the examples we discussed. If you completely understand the example code from class - you will do very well on the test!

  1. What is the output of the following program: 
    #include <iostream.h>

class blah {

public:
  static int a;	
  int b;


  blah(int x) {
    b=x;
    a=b+1;
  }

};


int blah::a = 0;


int main(void) {

  blah b1(5);
  blah b2(12);
  cout << "b1.a is " << b1.a << endl;
  cout << "b1.b is " << b1.b << endl;
  cout << "b2.a is " << b2.a << endl;
  cout << "b2.b is " << b2.b << endl;

}

  2. What is the output of the following program, and justify (explain) each line of output: 
    #include <iostream.h>

// Class ol_int is like an int but not quite!

class ol_int {
private:
  int x;

public:


  // default constructor - value is 0
  ol_int() {
    x=0;
  }


  // constructor from int
  ol_int(int v) {
    x=v;
  }


  // this is called when we assign an int to an ol_int
  ol_int& operator=( int i) {
    x=i;
    return(*this);
  }


  // overloaded plus operator
  // we return and int, but the compiler knows how to convert this
  // to an ol_int! (uses the constructor).
  // the return statement

  int operator+( ol_int &o) {
    return( x - o.x);
  }

  friend ostream &operator<<( ostream &, const ol_int& );



};


// Here is the definition of the overloaded << operator
// used to send the value of an ol_int to an output stream

ostream &operator<<(ostream &o, const ol_int &v) {
  o << v.x;
  return(o);
}


int main(void) {

  ol_int a=3;
  ol_int b=7;
  ol_int c,d;

  cout << "A is " << a << endl;
  cout << "B is " << b << endl;

  c = a + b;
  cout << "C is " << c << endl;

  d = 3 + 7;
  cout << "D is " << d << endl;

  ol_int e;
  cout << "E is " << e << endl;
  

}

  3. Write the definition of a class named "computer" which includes the attribute "name" (the name of the computer) and a print method that prints out this name.

    Also write the definition of a class named "Macintosh" that is derived from the class "computer" (computer is the base class) and includes the attribute "color" (a string) and a method named print that prints out the computer name and color.

    Here is main function that will test these objects, it uses a pointer to treat a Macintosh object as a computer object, and calls the print method. 

    int main() {
  computer *p;
  Macintosh imac("Joe's IMAC","Blue");

  p = &imac;

  p->print();
}
    I want the printout of this test program to be something like: 
    Name: Joe's IMAC
Color: Blue
    that it, I want the color printed out even though the computer class does not have any knowledge of the color attribute. (in other words - make sure your system is polymorphic).

Answers

  1. The output would be:

    b1.a is 13
b1.b is 5
b2.a is 13
b2.b is 12

    Since member a is a static member, all objects of type blah share a single a.

  2. The output would be:

    A is 3
    		 A is initialized from the integer 3, this calls the constructor that takes an int parameter. 
    B is 7
    		 B is initialized from the integer 7, this calls the constructor that takes an int parameter. 
    C is -4
    		 The ol_int + operator is overloaded to actually subtract! 
    D is 10
    		 The int + operator doesn't change. The integer addition happens normally, the result is assigned to the ol_int object. 
    E is 0
    		 The default constructor initializes the value to 0 

  3. 

class computer {
private:
   char *name;
 public:


   computer(char *n) {
     name = new char[strlen(n)+1];
     strcpy(name,n);
   }

   ~computer() {
     delete[] name;
   }


   virtual void print() {
     cout << "Name: " << name << endl;
   }
};

 
     



class Macintosh: public computer {
private:
   char *color;
 public:


   Macintosh(char *n, char *c) : computer(n) {
     color = new char[strlen(c)+1];
     strcpy(color,c);
   }

   ~Macintosh() {
     delete[] color;
   }


   void print() {
     computer::print();
     cout << "Color: " << color << endl;
   }
};