Expression Evaluation, Scope, Parameter Passing, Data Organization, Program Control, Binding

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Expression Evaluation, Scope, Parameter Passing,
Data Organization, Program Control, Binding

• By Ramon Quiusky
• CS 490
• Fall 2003

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Expression Evaluation

• Expressions are evaluated according to the
  precedence and order of their operators.
• Consider the following examples

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• Ex. 1

• Multiplication has the highest priority.
• Addition has the next highest precedence
• Left shift has the lowest precedence.

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• Ex. 2

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Scope

• Variables that are declared within the body of a
  function definition are said to be local to that
  function or to have that function as their scope.
• A variable within a function definition can have
  the same name of a variable within another
  function of main function definition (Static
  Scope).

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5 Types of Scope

• 1. Local scope a name declared within a block
  is
• accessible only within that block and
• blocks enclosed by it.
• int i

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• 2. Function scope Labels are the only names that
  have function scope. They can be used anywhere
  within a function, but are not accessible outside
  that function.
• 3. File scope Any name declared outside all
  blocks or classes has file scope. It is
  accessible anywhere in the translation unit after
  its declaration. Also known as Global Variables.

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• 4. Class scope Names of class members have class
  scope. Class member functions can be accessed
  only by using the member-selection operators (.
  or gt) or pointer-to-member operators (. or gt)
  on an object or pointer to an object of that
  class.
• 5. Prototype scope Names declared in a function
  prototype are visible only until the end of the
  prototype. The following prototype declares two
  names (szDest, szSource) these names go out of
  scope at the end of the prototype
• char strcpy( char szDest, const char
  szSource )

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Parameter Passing

• Two main parameter types
• Call-by-value
• Call-by-reference
• But first, what are formal parameters and
• arguments?

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• Formal Parameter a kind of blank space holder
  that is filled in with something when the
  function is called. They are listed in a function
  prototype and used in the body of a function
  definition.
• Argument something that is used to fill in a
  formal parameter. When a function call is
  execute, the arguments are plugged in for the
  formal parameters.

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• Example
• //libraries (I/O, math, etc)
• //prototype
• int sum(int a, int b)
• //
• //main function
• //function call
• cout ltlt Sum ltlt sum(24, 25) ltlt endl
• //
• int sum(int a, int b)
• return (ab)

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• Call-by-value a formal parameter that when
  listed in the prototype of a function there is no
  ampersand () attached to its type
  specification
• ex
• int sum(int a, int b)

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• 2. Call-by-value a formal parameter that when
  listed in the prototype of a function there is an
  ampersand () attached to its type
  specification

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• include ltiostream.hgt
• void get_number(int input1, int input2)
• void show_results(int output1, int output2)
• int main()
• int first_num, second_num
• get_number(first_num, second_num)
• show_results(first_num, second_num)
• return 0
• void get_number(int input1, int input2)
• cin gtgt input1
• cin gtgt input2

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• Functions can also be used as parameters.
• Ex. //function call
• sum(get_first_num(), get_sec_num())
• int sum(int a, int b)
• return (ab)
• int get_first_num()
• int a cingtgta return a
• int get_sec_num()
• int b cingtgtb return b

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Constructs for Data Organization

• What is a data structure?
• An organization of information, usually in
  memory, for better algorithm efficiency, such as
  queue, stack, linked list, heap, dictionary, and
  tree, or conceptual unity, such as the name and
  address of a person. It may include redundant
  information, such as length of the list or number
  of nodes in a subtree.

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• Static Data Structure size determined when a
  program is compiled
• Dynamic Data structure size determined when a
  program is actually running rather than at
  compilation time
• Pointers enable us to define this type of data
  structure

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• Other types of data structures
• external memory data structure
• passive data structure
• active data structure
• persistent data structure
• recursive data structure
• See http//www.nist.gov/dads/ for definitions

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Program Organization

• Program Organization
• A collection of program units constitutes an
  executable program. Program units can contain
  other smaller units.
• A program consists of the following (from a
  Fortran Program)
• Main program
• External subprogram (subroutine or function)
• Module
• Block data

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Program Control

• It is good practice to break a program down into
  pieces that can be thought of independently. Once
  the program has been completed, we can think of
  its execution as being a series of these pieces
  that work together in a certain sequence. These
  pieces then pass the control of the program
  between each other.

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• Examples
• if-else Statements
• while Loops
• for Loops
• continue Statement
• break Statement

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• Nesting Control Statements
• if (my_money gt cost_of_CD)
• then buy_CD
• Else
• if (see_a_friend)
• then borrow_money
• else get_a_job

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Binding

• Linking between messages and methods
• Early Binding Static binding. Binding of
  functions at compile time
• AddRealNums (x, y) x y are of type real
• Late Binding Late Binding. Binding of message
  selector to the appropriate method at run time
• AddNumber(x, y) x y are number objects

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• Static Type what can be determined at compile
  time
• Dynamic Type actual type as determined during
  run time.

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Static Binding Vs Dynamic Binding

• Static binding binding based on static type
• More efficient
• Less flexible
• Static type checking leads to safer programs
• Dynamic Binding
• More flexible
• Less efficient
• May need dynamic type checking

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Resources

• Data Structures and other objects using C -
  Savitch
• Problem Solving with C - Savitch
• Java How to Program Deitel Deitel
• http//www.csd.uu.se/kurs/oop/ht98/Lectures/D5/htm
  l/Dynamic_Binding/sld019.htm
• http//msdn.microsoft.com/library/
• http//www.nist.gov/dads/