C and

1
C and Object-Oriented Programming Basic
Program Coding
2
Basic Program Coding

• Goals of this Lesson
• Understand how to reuse existing code in your
  programs (using include)
• Obtain input data from the user and display
  information to the user (with cin and cout)
• Evaluate and create arithmetic expressions
• Understand operations common to many objects
  (such as int, double, and string)
• Construction, Output, Assignment, and Input

3
The C Programming Language A Start

• A C program is a human-readable sequence of
  characters, usually created with a text editor
  and stored as a file.
• this is the source code
• The filename has specific extension
• .cc or .C or.cpp
• others too

4
General Forms

• General forms provide information to create
  syntactically correct programs
• Anything in yellow boldface must be written
  exactly as shown (cout ltlt for example)
• Anything in italic represents something that must
  be supplied by the user
• The italicized portions are defined elsewhere

5
General Form A program

• // Comments
• include-directive(s)
• int main()
• object-initializations
• statement(s)
• return 0

// Comments include-directive(s) void
main() object-initializations
statement(s)
6
Example C Program

• // This C program gets a number from the
• // user and displays that value squared
• include ltiostream.hgt // for cout cin endl
• int main()
• double x 0.0
• cout ltlt "Enter a number "
• cin gtgt x
• cout ltlt "x squared " ltlt (x x) ltlt endl
• return 0

7
The Compiler

• The compiler
• reads source code in a character by character
  fashion (tokenization)
• reports errors whenever possible
• reports warnings to help avoid errors
• conceptually replaces include with the source
  code of the include file

8
include Directives

• General form include - directive
• include ltinclude-filegt
• -or-
• include "include-file"
• lt gt causes a search of the system folder(s)
• these files should be found automatically.
• The form with " " first searches the working
  folder before searching the system folder(s)
• the " " indicates an author supplied file name
  that you may need in your working folder

9
The Smallest Pieces of a C Program

• A token is the smallest recognizable unit in a
  programming language.
• There are four types of tokens
• special symbols
• keywords
• identifiers
• constants

10
A "tokenized program"

• Each color represents either a different token
  special symbol reserved word identifier
  constant comment (gray), or include directive
  (cyan)
• // Comment This is a complete C program
• include ltiostreamgt
• using namespace std
• int main()
• cout ltlt "Hello World!"
• return 0

11
Special Symbols

• One or two character sequences (no spaces).
• // lt gt ( ) ltlt !
• Some special symbols mean different things in
  different contexts.

12
C Keywords

• Word like tokens with a pre-defined meaning that
  can't be changed (reserved)
• double int
• Some of the keywords in the text
• bool class for operator typedef
• case do if return void
• char else long switch while

13
Identifiers

• There are some standard (must be available with
  the C compiler) identifiers
• endl sqrt string width std
• The programmer can make up new identifiers
  (programmer-defined)
• test1 x1 aNumber MAXIMUM A_1
• Note main is a programmer-defined identifier,
  cout is a standard identifier

14
Self-Help Exercise

• Identifiers have from 1 to 32 characters
• 'a'..'z', 'A'..'Z', '0'..'9', '_'
• identifiers should start with a letter a1 is
  legal, 1a is not (can also start with underscore
  _ )
• C is case sensitive. A and a are different.
• Which of these are valid identifiers?
• a) abc e) ABC i) a_1
• b) m/h f) 25or6to4 j) student Number
• c) main g) 1_time k) string
• d) double h) first name l) ______

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Constants

• floating-point constants
• 1.234 -12.5 0.0 0. .0 1e10 0.1e-5
• string constants
• "character between double quotes"
• integer constants
• -1 0 1 -32768 32767
• character constants
• 'A' 'b' '\n' '1'

16
Comments

• Example comments
• // on one line
• /
• between slash star and star slash
• /
• Provide internal documentation
• Helps us understand program that we must
  read--including our own.
• Can be used as "pseudocode" within a program and
  later changed into C or left as is to provide
  documentation

17
Common Operations on Objects

• Common Operations for many classes of objects
  include these four
• Declaration Construct an object
• Initialization or optionally initialize its
  state
• Assignment Modify the state of an object
• Input Modify the state of an object
• Output Inspect the state of an object

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Object Constructions

• Use default initial state double is garbage
• class-name identifier
• -or-
• class-name identifier , identifier ,
  , identifier
• Allow client to supply initial state
• class-name identifier initial-state
• -or -
• class-name identifier ( initial-state )
• -or -
• class-name identifier initial-state ,
  identifier ( initial-state )
• , , identifier
  initial-state

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Examples Object Constructions

• Construct seven objects qualityPoints is
  undefined
• double credits 15.5, qualityPoints
• string firstName, lastName("Harrison")
• double x 0.0, y 0.0
• double z // garbage state (unknown)
• Note strings have the default value of the null
  string "", which has 0 characters.
• A double object has no default value--it's
  garbage unless an initial value is supplied.

20
Output with cout

• Programs must communicate with users
• This can be done with keyboard input statements
  and screen output statements
• A C statement is composed of several components
  properly grouped together to perform some
  operation.
• Here is the first statement used to display
  constants and object state to the screen

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The cout Statement

• The general form of a cout statement
• cout ltlt expression-1 ltlt expression-2 ltlt
  expression-n
• Example
• cout ltlt "Grade " ltlt courseGrade ltlt endl

22
What happens with cout?

• When a cout statement is encountered, the
  expressions are displayed on the screen in a
  manner appropriate to the expression.
• New Lines with endl
• When encountered in a cout statement, endl
  generates a new line on the monitor
• To properly use cout and endl, your program must
  have this code at the top of the file
• include ltiostreamgt // for cout and endl
• using namespace std

23
Self-Help Exercise Write the output generated
by this program

• include ltiostream.hgt // for cout
• int main()
• double aDouble 0.0
• cout ltlt "12345678" ltlt endl
• cout ltlt (2.5 3) ltlt (23) ltlt endl
• cout ltlt aDouble
• return 0
• Output?

24
Assignment

• Certain objects have undefined state
• double dunno, do_you
• cout ltlt dunno ltlt endl // Output? ______
• The programmer can set the state of objects with
  assignment operations of this form
• object-name expression
• Examples
• dunno 1.23
• do_you dunno - 0.23

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Memory before and after

• Object Old Modified
• Name State State
• dunno ? 1.23
• do_you ? 1.0
• The expression must be a value that the object
  can store (assignment compatible)
• dunno "Ohhh no, you can't do that" //
  lt-Error
• string s
• s 1.23 // lt-Error

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Self-Help Exercise

• Write the values for bill and name
• double bill
• string name
• bill 10.00
• bill bill (0.06 bill)
• name "Bee Bop"
• name "Hip Hop"
• // bill is ___________?
• // name is now ________?

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Input with cin

• General forms
• cin gtgt object-1
• -or-
• cin gtgt object-1 gtgt object-2 gtgt object-n
  
• Example cin gtgt test1
• When a cin statement is encountered
• the program pauses for user input.
• the characters typed by the user are processed
• the object's state is changed to the value of the
  input

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Input is separated with Whitespaceblanks, tabs,
and newlines

• include ltiostream.hgt // for cout, cin, endl
• include string.h // for class string
• int main()
• string name
• cout ltlt "Enter your name "
• cin gtgt name
• cout ltlt "Hello " ltlt name
• return 0
• Dialogue when the user enters Kim McPhee
• McPhee is still waiting to be processed by a
  non-existent future cin statement
• Enter your name Kim McPhee
• Hello Kim

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Arithmetic Expressions

• Arithmetic expressions consist of operators such
  as - / and operands such as 1.0, payRate,
  and hoursWorked
• Example expression used in an assignment
• grossPay payRate hoursWorked
• Another example expression
• (40payRate) 1.5payRate(hoursWorked-40)
• The previous expression has how many
• operators ?___ ?
• operands ?___ ?

30
Arithmetic Expressions
An arithmetic expression can be written in these
forms
a numeric object x or a numeric
constant 100 or 99.5 or expression
expression 1.0 x or expression -
expression 2.5 - x or expression
expression 2 x or expression / expression
x / 2.0 or ( expression ) (1 2.0)
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Precedence of Arithmetic Operators

• Expressions with more than one operator require
  some sort of precedence rules
• / // evaluated left to right order
• - // evaluated left to right order
• What is 2.0 4.0 - 6.0 8.0 / 6.0 ____?
• Use (parentheses ) for readability or to
  intentionally alter an expression
• double C
• double F 212.0
• C 5.0 / 9.0 (F - 32) // C _____?

32
Self-Help Exercise Write the complete dialogue
with input 2.3 5.0 2.0

• include ltiostream.hgt // for cin, cout, and endl
• int main()
• // Declare Objects
• double x, y, z, average
• // Prompt for and get input from the user
• cout ltlt "Enter three numbers "
• cin gtgt x gtgt y gtgt z
• // Process
• average (x y z) / 3.0
• // Output
• cout ltlt "Average " ltlt average ltlt endl
• return 0

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const objects

• It is sometimes convenient to have objects that
  cannot have altered state.
• const class-name identifier expression //
  use this form
• -or-
• const class-name identifier ( expression )
  
• Examples
• const double PI 3.1415926
• const string ERROR_MESSAGE "Nooooooo"
• Errors
• PI 9.8
• cin gtgt ERROR_MESSAGE

34
Another Algorithm Pattern Prompt then Input

• The Input/Process/Output programming pattern can
  be used to help design many programs in the first
  several chapters
• The Prompt then Input pattern also occurs
  frequently.
• The user is often asked to enter data
• The programmer must make sure the user is told
  what to enter

35
Prompt then Input Pattern
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Examples

• Instances of the Prompt then Input pattern
• cout ltlt "Enter your first name "
• cin gtgt firstName
• cout ltlt "Enter accumulated credits "
• cin gtgt credits
• Write code that gets the current temperature from
  the user
• ? ________ ?

Optional Demo average3.cpp to see prompt then
input used three times