Creation of new Variables

Static allocation: using declaration statements - allocated before program begins execution( fortran,
C global variables)

Automatic allocation: using declaration statements - automatically allocated on entering scope- stack based storage management(Pascal local variables)

Dynamic allocation: using explicit directives - may not be automatic - heap-based storage management
 

                                        Storage management Approach

Explicit management by programmer:programmer must return unneeded memory to system like

C++ delete, object pascal dispose

Advantage: efficiency

Disadvantages:

•  attempted use of memory not yet allocated or already freed
•  multiple freeing of memory
•  memory leak - allocated memory is never released

Advantage: safety and convenience

disadvantage: relative inefficiency
 

                                         Syntax for Automatic creation

In C++ and object Pascal (and sometimes in objective-C) memory for variables is often created using a simple declaration statement.

Card aCard;      //  C+ +   declaration

var
   aCard : Card;     { object -pascal declaration }
 

                                        Syntax for Dynamic creation

Always i smalltalk and sometimes in other languages, objects are created dynamically using the "new" operator.

    d <== Card new.

    aCard = new Card;

    aCard = new Card(Card.spade,5);