CSCI101 An Introduction to Programming using C

1
CSCI101 An Introduction to Programming using
C
2
Functions 1
3
Procedural Abstraction and Functions that Return
a Value
4
Contents of Functions 1

• 0 Introduction to Functions
• 1 Top-Down Design
• 2 Predefined Functions
• 3 Programmer-defined Functions
• 4 Procedural Abstraction
• 5 Local Variables
• 6 Overloading Function Names

5
Introduction to Functions

• Programs are normally made up of subparts.

6
Introduction to Functions

• There may be a subpart to handle data input,
• another subpart to handle the processing of
  the data
• and another subpart to handle data output. . .

7
Introduction to Functions

• These subparts or subprograms are given a name
  and are considered as a separate entity. They are
  known as functions.
• Functions are executed simply by calling their
  name.

8
Introduction to Functions

• Functions can receive data to be processed
  within the function, and . . .

9
Introduction to Functions

• . . . functions can return data to the part of
  the program that called the function.

10
Introductory Example ProgramsRunning under
Dev-C

• funcs00.cpp - example program with no functions
• funcs01.cpp - using a function
• funcs02.cpp - passing an int to a function
• funcs03.cpp - passing an int and a double
• funcs04.cpp - returning a value back from a
  function
• funcs05.cpp - using the predefined function
  sqrt()
• funcs06.cpp - using a global constant

11
Introductory Example ProgramsRunning under
Borland version 5.02

• funcs00_Borland.cpp - example program with no
  functions
• funcs01_Borland.cpp - using a function
• funcs02_Borland.cpp - passing an int to a
  function
• funcs03_Borland.cpp - passing an int and a
  double
• funcs04_Borland.cpp - returning a value back
  from a function
• funcs05_Borland.cpp - using the predefined
  function sqrt()
• funcs06_Borland.cpp - using a global constant

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A program with no functions

• http//www.annedawson.com/funcs00.cpp

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A program which uses a function
http//www.annedawson.com/funcs01.cpp
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Passing an int to a function
http//www.annedawson.com/funcs02.cpp
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Passing an int and a double to a function
http//www.annedawson.com/funcs03.cpp
16
Returning a value back from a function

• http//www.annedawson.com/funcs04.cpp

17
Using the predefined function sqrt()

• http//www.annedawson.com/funcs05.cpp

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Using a global constant

• http//www.annedawson.com/funcs06.cpp

19
Contents of Functions 1

• 0 Introduction to Functions
• 1 Top-Down Design
• 2 Predefined Functions
• 3 Programmer-defined Functions
• 4 Procedural Abstraction
• 5 Local Variables
• 6 Overloading Function Names

20
Top-Down Design

• Top-down design is breaking down a problem
  into smaller and smaller problems, until the
  smallest problem can be implemented in a function
  in C which fits onto a single screen of the
  code editor...

21
Top-Down Design

• Program design known as structured program
  design or top-down program design requires that
  programming problems are broken down into small
  problems which are executed one at a time. . .

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Top-Down Design

• The goal of top-down design is to break a
  problem into individual tasks, or modules, that
  can easily be transcribed into pseudocode,
  flowcharts or a program.

23
Top-Down Design
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Top-Down Design

• Modules continue to be broken down into
  further modules, until at the lowest level, the
  modules are small enough to be coded into a
  single function which performs a single task.

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Structured Programming

• A structured program is one which is based on
  a modular design and uses only the three types of
  control structures sequences, decisions and
  loops

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Advantages of Structured Programs

• Easy to write
• Easy to debug
• Easy to understand
• Easy to change

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Contents of Functions 1

• 0 Introduction to Functions
• 1 Top-Down Design
• 2 Predefined Functions
• 3 Programmer-defined Functions
• 4 Procedural Abstraction
• 5 Local Variables
• 6 Overloading Function Names

29
Predefined Functions

• We have already seen the use of the predefined
  function sqrt()in program

http//www.annedawson.com/funcs05.cpp
30
Predefined Functions

• Predefined functions are provided for you by
  the C language.

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Predefined Functions

• The definitions of predefined functions (the
  predefined function code - the C statements
  which make up the functions) are contained in a
  library header file.

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Predefined Functions

• The header file must be included in your
  program code with a include statement

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sqrt() - square root function

• Receives a double argument
• Returns a double value
• Example sqrt(4.0)
• Value 2.0
• Library ltmath.hgt or ltcmathgt
• Example program Display 4.1 page 183

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Contents of Functions 1

• 0 Introduction to Functions
• 1 Top-Down Design
• 2 Predefined Functions
• 3 Programmer-defined Functions
• 4 Procedural Abstraction
• 5 Local Variables
• 6 Overloading Function Names

35
Programs which use Programmer-defined functions

• funcs00.cpp - example program with no functions
• funcs01.cpp - using a function
• funcs02.cpp - passing an int to a function
• funcs03.cpp - passing an int and a double
• funcs04.cpp - returning a value back from a
  function
• funcs05.cpp - using the predefined function
  sqrt()
• funcs06.cpp - using a global constant

36
Contents of Functions 1

• 0 Introduction to Functions
• 1 Top-Down Design
• 2 Predefined Functions
• 3 Programmer-defined Functions
• 4 Procedural Abstraction
• 5 Local Variables
• 6 Overloading Function Names

37
Procedural Abstraction

• treating functions as black boxes
• also known as information hiding
• also known as procedural abstraction
• it means that the function prototype and its
  comments should be all a programmer needs to know
  in order to use the function
• All variables used by the function should be
  declared inside the function

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Implementation of Procedural Abstraction

• You can save your function definitions in a
  separate file, and compile the file separately,
  before linking it to the other files to generate
  the executable file.

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Implementation of Procedural Abstraction

• The file that contains the main function of the
  program also contains just the functions
  prototypes.

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Implementation of Procedural Abstraction

• This way, you can hide the details of the
  functions, maintaining procedural abstraction.

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Contents of Functions 1

• 0 Introduction to Functions
• 1 Top-Down Design
• 2 Predefined Functions
• 3 Programmer-defined Functions
• 4 Procedural Abstraction
• 5 Local Variables
• 6 Overloading Function Names

42
Local Variables

• Variables that are declared inside a function
  definition are known as local variables.
• A variable of the same name in the main
  function is a different variable!

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Local Variables

• A functions call-by-value formal parameters
  are variables which are local to the function
  definition. . .
• in other words, they are local variables

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Scope

• The scope of a variable is that part of the
  program where it can be used.

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Local and Global Scope
http//www.annedawson.com/funcs07.cpp
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Local Scope

• http//www.annedawson.com/local.cpp

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Global Scope

• http//www.annedawson.com/global.cpp

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Global constants

• const double PI 3.142
• int main ()

Good!
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Global Constant

• http//www.annedawson.com/constant.cpp

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Global variables

• // DO NOT DO THIS
• int number 10
• int main ()

Bad!!!!!
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Contents of Functions 1

• 0 Introduction to Functions
• 1 Top-Down Design
• 2 Predefined Functions
• 3 Programmer-defined Functions
• 4 Procedural Abstraction
• 5 Local Variables
• 6 Overloading Function Names

52
Overloading Function Names

• If you have two or more function definitions
  for the same function name, that is called
  overloading.

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Overloading Function Names

• When you overload a function name, the
  function definitions must have different numbers
  of formal parameters, or some formal parameters
  of different data types.

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Calling an overloaded function

• When there is a function call, the compiler
  uses the function definition whose number of
  formal parameters and types of formal parameters
  match the arguments in the function call.

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Overloaded function program

• Display 4.16 on page 230

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Polymorphism

• Polymorphism means many forms and is an
  important term in C. Function overloading is
  our first example of polymorphism.

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End of CPP_Functions1.ppt
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• Last updated Friday 24th March 2006, 1347 PT,
  AHD