The Command Line, Classes

Tom Kelliher, CS 320

Mar. 10, 2000

Administrivia

Announcements

Don't forget \\ phoenix.

Jill's environment class???

Save copies of files before making changes.

Make a few changes; test.

Assignment

Implement stack class, as defined by stack.h. Develop a set of tests for the class.

From Last Time

Outline

1. Using command line arguments.

2. Classes: why, sum, stack.

Coming Up

Maze design.

The Command Line

1. Setting them from the IDE:

   Project | Settings | Debug | Program arguments
   

   Example: 20 30
   No commas.

2. Accessing command line args from main():

   int main(int argc, char *argv[])
   {
      /* ... */
   
      return 0;   /* "Normal" return value. */
   }
   

   argc, argv (argv[0] --- program name)?

3. atoi() --- stdlib.h.

Classes

Why?

1. Abstract data types. Improvement over the primitive types.

2. Data hiding.

3. Implementation hiding.

Sum

• An abstract class representing the sum of two numbers.

• What data member(s) will it need?

• What methods?

sum.h:

#ifndef SUM_H
#define SUM_H

class sum
{
 private:   // Default protection.  Also protected.

   int theSum;

 public:

   sum(int, int);
   int get(void);
};

#endif

sum.cpp:

#include "sum.h"

sum::sum(int a, int b)
{
   theSum = a + b;
}

int sum::get(void)
{
   return theSum;
}

main.cpp:

#include <iostream.h>
#include "sum.h"

int main()
{
   sum s(12, 34);
   sum t(-90, 85);

   cout << "sum s: " << s.get() << endl;
   cout << "sum t: " << t.get() << endl;

   return 0;
}

Implement, build, and run.

Stack

• The ``standard'' integer stack ADT.

• Operations? (push, pop, full, empty).

  push and pop should use full and empty, respectively.

• Twist 1: User specifies the size of each stack. Dynamic allocation within constructor, requiring use of the destructor.

  // In the class declaration:
  int *s;
  
  // In the constructor:
  if (!(s = new int[size]))   // Should always check return values!!!
     die("Couldn't allocate space for stack.\n");
  
  // In the destructor:
  delete [] s;   // Remind compiler that s is a pointer.
  

• Twist 2: A private function: die():

  void stack::die(char *s)
  {
  	cout << s;
     exit(1);   // "Abnormal" return value.  exit() from stdlib.h.
                // Why can't I just use return?
  }
  

• What data members?

stack.h:

#ifndef STACK_H
#define STACK_H

class stack
{
 private:

   int* s;
   int size;
   int tos;

   void die(char *);

 public:

   stack(int);
   ~stack();
   void push(int);
   int pop(void);
   int full(void);
   int empty(void);
};

#endif