Assignment #5

Pengajar : Tri Djoko Wahjono

Review Question :

11.   What are the advantages and disadvantages of dynamic type binding?

         =>

         The advantage is flexibility (generic program units).

12. Define static, stack-dynamic, explicit heap-dynamic, and implicit 

      heap-dynamic variables.What are their advantages and disadvantages?

         =>

Static: bound to memory cells before execution begins and remains bound to the same memory cell throughout the execution.

Stack-dynamic: storage bindings are created for variables when their declaration statements are elaborated.

Explicit heap-dynamic: allocated and deallocated by explicit directives, specified by the programmer, which take effect during execution.

Implicit heap-dynamic variables: Allocation and deallocation caused by assignment statements.

13. Define lifetime, scope, static scope, and dynamic scope.

      =>

      Lifetime: A time during which the variable is bound to a specific memory location. The lifetime begins when it is bound to a specific cell and ends when it is unbound from that cell.

      Scope: The range of statements in which the variable is visible. A variable is visible in a statement if it can be referenced in that statement.

      Static scope: is based on program text and to connect a name reference to a variable , you (or the compiler) must find the declaration.

      Dynamic scope: Based on calling sequences of program units, not their textual layout (temporal versus spatial). References to variables are connected to declarations by searching back through the chain of subprogram calls that forced execution to this point.

14. How is a reference to a nonlocal variable in a static-scoped program 

      connected to its definition?

       =>   A reference to a non-locally variable in a static-scoped language with nested subprograms requires a two step access process:

1. Find the correct activation record instance

2. Determine the correct offset within that activation record instance

15. What is the general problem with static scoping?

         => Usually too much access. Scope structure destroyed as program 

               evolves.

Problem  Set :

1. Which of the following identifier forms is most readable? Support your 

    decision.

      sumOfSales

   sum_of_sales

   SUMOFSALES

     => I'm choose sum_of_sales, because it's easier to see the spaces 

          between words and easier to read.

2. Some programming languages are typeless. What are the obvious 

    advantages and  disadvantages of     having no types in a language.

=>

* Advantages : allow users to write sloppy programs faster.

     * Disadvantages : cannot control the data and variables, compiler cannot detect any mistake.

3. Write a simple assignment statement with one arithmetic operator in some language you know. For each component of the statement, list the various bindings that are required to determine the semantics when the statement is executed. For each binding, indicate the binding time used for the language.

=> (C++)

int count;count = count + 5;

Possible types for count: set at language design time. Type of count: bound at compile time.
Set of possible values of count: bound at compiler design time. Value of count: bound at execution time with this statement. Set of possible meanings for the operator symbol ““:*bound at language definition time.*Meaning of the operator symbol “” in this statement: bound at compile time.
Internal representation of the literal “5”: bound at compiler design time.

4. Dynamic type binding is closely related to implicit heap-dynamic 

    variables. Explain this relationship.
    => Both are related to the assignment and the statement.

5. Describe a situation when a history-sensitive variable in a subprogram is
    useful.

    =>History sensitive variables may be useful in data manipulation 

        subprograms, where some operation is performed on a variable, and 

        the function exits, then the function is called again. This way, 

        the function doesn't have to take the variable as a parameter, but only
        to return it.