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IntStack Sample

1. Questions About IntStack Homework
2. Outline of Programming Steps
3. Step 1. main.cpp
4. Step 2. IntStack.h
5. Step 3. IntStack.cpp

1. Questions About IntStack Homework

• I am receiving many questions regarding the IntStack assignment.

• At the last lecture I made a small demo sample, "IntStack for beginners".

• You can download sample code in one ZIP file: IntStack_4_beginners.zip

• Once downloaded, start a new C++ project, then add main.cpp and IntStack.cpp files to your project's list of source files.

   

2. Outline of Programming Steps

• Below is a short outline of steps that I used to put this sample together in class.

   

3. Step 1. main.cpp

• Initially, I wrote a small main program, imagining that I already have a working stack object:

  
  // main.cpp
  #include "IntStack.h"
  
  int main()
  {
  	IntStack st;
  	st.reset();
  
  	int x = 999;
  	st.push( x );
  	
  	int y;
  	y = st.top();
  
  	st.pop();
  
  	return 0;
  }
  
  

• As you can see, for this to be functional, we need to define what "IntStack" is.

   

4. Step 2. IntStack.h

• Defining "IntStack" is the job of IntStack.h.

• In IntStack.h file we have a class that behaves like a stack of integers.

• It is pretty simple (I did this without looking at the assignment requirements, so if you use this sample to start your homework, be ready to make changes in function parameters and return types.)

  
  // IntStack.h
  class IntStack {
  public:
      static const int STACK_SIZE = 100;
  
  private:
      int m_array[ STACK_SIZE ];
      unsigned int m_sp;
  
  public:
      // public interface of the stack:
      void push( int element );
      int top();
      void pop();
      unsigned int size();
      void reset();
  
  };//class IntStack
  
  

• What you see here is the C++ header file, not the source file.

• Header files don't have any executable code.

• Header files declare constants, variables, classes, and functions, but do not contain any actual code that is typically found inside function bodies.

   

5. Step 3. IntStack.cpp

• So far our class IntStack has only data members and a set of member function declarations.

• Therefore, the bodies of these functions must be defined elsewhere.

• Because may I want to use IntStack in other projects, I am creating a separate file that contains the member function definitions.

• For sanity reasons, I named the new file IntStack.cpp, so the name suggests its purpose:

  
  // IntStack.cpp
  #include <iostream>    // needed for std::cerr
  #include "IntStack.h"
  
  void IntStack::reset()
  {
  	m_sp = 0;
  }
  
  void IntStack::push( int element )
  {
  	// before:
  	// [] [] [] [] [] []
  	//        |
  	//       m_sp
  	//
  	// after:
  	// [] [] [e] [] [] []
  	//            |
  	//           m_sp
  	//
  	m_array[ m_sp ] = element;
  	++m_sp;
  }
  
  int IntStack::top()
  {
  	if ( m_sp == 0 ) {
  		std::cerr << "stack is empty!";
  		return -1;
  	}
  	return m_array[ m_sp - 1 ];
  }
  
  void IntStack::pop()
  {
      // Not implemented
  }
  
  unsigned int IntStack::size()
  {
  	return m_sp;
  }
  
  

• Note that I didn't implement all of it, only push, top, and size.

• The above file, IntStack.cpp is a C++ source file, also known as C++ implementation file.

• This means that is is compiled separately from main.cpp.

• The linker makes executable image of the program by combining the results of the two source files in my project.

• Notice that my version of push never checks if the stack is full (apparently, when m_sp == STACK_SIZE.) So you should add this check to the code yourself.

• Also, std::cerr is very much like std::cout and represents the standard output stream for errors

• std::cerr should be used when you print information about program errors.

• As other stream objects, std::cerr comes from iostream standard library header:

  
  // IntStack.cpp
  #include <iostream>
  // ...
  
  

• One final note that each function name is prefixed by IntStack::

  
  // IntStack.cpp
  // ...
  void IntStack::push( int element )
  {
      //...
  }
  
  

  This is because our functions come from the scope of class IntStack. In other words, these funtions are not part of the global scope. The only function declared in global scope is the main entry into our program. The two-colon operator " :: " is the scope resolution operator.