• Need to include array.h
• compiler_array.cpp needs the array declaration
  • Need the name (Array) for scope resolution (Array::)
  • Need the function declarations in order to implement them
  • Need the data members in order to work with them
• compiler_array.cpp does not need main.cpp
• Compile main.cpp (compiler_main.cpp)
  • Need to include array.h
  • compiler_main.cpp needs
    • to know the size of the Array object, when main.cpp contains an Array declaration
    • to know the functions of Array when main.cpp calls an Array function
  • compiler_main.cpp does not need to know about array.cpp
    • We can thus develop our main even before we have fully implemented our class!
  • Link the program
    • Need main.o and array.o

Adding a #Include Guard (Macro Guard)

• Preventing multiple inclusions of the same .h file

• The code

      	class C {
      		...
      	};
      	...
      	class C {
      		...
      	};
      

  is illegal.
• This presents the following problem:

      file student.h
      ...
      #include "array.h"  // for the array of courses below
      ...
      
      class Student {
      	...
      private:
      	...
      	Array courses(100);
      };
      
      ------------------
      
      file main.cpp
      ...
      #include "student.h"		// We're a student application
      #include "array.h"		//  For the array of students below
      ...
      
      Array student(1000);		
      
      ...
      			

  The above code has the same duplicate class definition problem
• To prevent this, we prevent the same .h file from being included more than once
  • Introduce a preprocessor variable name deriving from the .h file name
    • By convention, its the file name in caps followed by _H
  • Use the preprocessor's conditional compilation facility to check whether the file has already been included and skip it if it has

      				#ifndef ARRAY_H			// if ARRAY_H has not already been defined
      				#define ARRAY_H			// define it
      					...
      				#endif 
        			

• Platform-dependent code
• Development/production phase code