Connecting with Computer Science, 2e

1
Connecting with Computer Science, 2e

• Chapter 15
• Programming II

2
Objectives

• In this chapter you will
• Gain an understanding of the basics of high-level
  programming languages, using Java and C as
  examples
• Learn about variable types in Java and C and
  how theyre used
• Explore the different control structures in Java
  and C

3
Why You Need to Know About... Programming
Languages

• Time, money, and effort go into learning computer
  programming languages
• The only real way to learn is practice, practice,
  and more practice
• After reading this chapter, you must sit down at
  the computer and practice the concepts frequently

4
Java and C Programming Languages

• Criteria for choosing a programming language
• Tasks to perform
• Programmers skill level
• Programs lifetime
• Software complexity being designed
• C and Java characteristics
• Support an object-oriented environment
• Usable on different operating systems
• Provide strong foundation for learning how to
  program
• Provide a springboard to other languages

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Learning to Cook with Java and C

• Four ingredients to write programs
• Variables
• Operators
• Control structures
• Objects
• Java and C high-level programming languages
  provide computer interaction
• Without speaking in binary 1s and 0s

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Learning to Cook with Java and C (contd.)

• Java history
• Designed for Internet use
• Introduced by Sun Microsystems in 1995
• Intended for small tasks or small applications
  (i.e., applets)
• No need to write entire programs
• Developed into full-blown programming language
• Language of choice to develop communication
  devices and media applications (e.g., PDAs, cell
  phones, Internet, and networks)

7
Learning to Cook with Java and C (contd.)

• Javas advantages
• Uses familiar syntax
• Very portable
• Powerful and popular
• C history
• Created by Bjarne Stroustrup at Bell Labs in 1983
• Based on C with added features
• Object-oriented programming language
• Offers simplified memory management and access to
  low-level memory

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Variables

• Have specific effects on a programs outcome
• Must have an identifier or name prior to use
• Declaration statement associating an identifier
  with a variable, an action, or another
  programming element
• When declared, you specify attributes
• Identifier (name)
• Type (character, numeric, Boolean, and so forth)
• Content
• Example int numTicketsBought

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Variable Naming Conventions

• Rules for declaring a variable in Java or C
• Use only letters, underscores, numbers
• Begin name with a letter
• Avoid Java and C reserved words
• Reserved word
• Keyword with a specific instructional meaning
• Name cannot be used for a variable
• Programming language already using it as an
  instruction

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Variable Types

• Java and C are strongly typed
• Must declare type of data a variable can hold
• Major Java data types
• Six number-related data types
• One character related
• One for true and false (Boolean)
• Major C data types
• Adds a type for signed or unsigned numbers
• Syntax for declaring a variable
• type variableName

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Integer Data Types

• Used for positive and negative whole numbers
• Java example
• int studentTickets
• short studentFees
• long studentTuition
• byte studentGrade
• C example
• int studentTickets
• short int studentFees
• unsigned int totalPoints

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Integer Data Types (contd.)
Table 15-1, Java integer data types
Table 15-2, C integer data types
13
Floating-Point Data Types

• Used for positive and negative numbers containing
  decimals
• Examples of declaring variables in both
  languages
• float salary
• double billGatesSalary

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Floating-Point Data Types (contd.)
Table 15-3, Java floating-point data types
Table 15-4, C floating-point data types
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Character Data Type

• Used for variables holding only one character
• Example char studentMiddleInit

Table 15-5, Java character data type
Table 15-6, C character data types
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Boolean Data Type

• Used for only one of two values true or false
• Java and C
• Cannot associate a number with a Boolean value
• Rely on true or false
• Java Boolean variable declaration
• boolean deserveRaise
• C Boolean variable declaration
• bool deserveRaise

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Boolean Data Type (contd.)
Table 15-8, C Boolean data type
Table 15-7, Java Boolean data type
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String Data Type

• Stores a piece of information
• Not a number
• Contains more than one character
• Declared using double quotes
• Uses the String or string keywords
• Examples of an empty string
• String sName //Java String
• string sName //C string

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String Data Type (contd.)

• Examples of a string with contents assigned
• String sName "Joe Blow" //Java
• string sName "Joe Blow" //C
• Concatenation operator
• The () operator
• Process of combining or joining strings into one
  value
• See example code on pages 517518

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Hungarian Notation

• Variable-naming method
• Adds a letter at the beginning of a variable name
• Indicates data type

Table 15-9, Hungarian notation examples
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Variable Content

• When variable is declared
• Use an equal sign () to assign a value
  immediately
• Variable initialization supplying value when
  variable is first declared
• Do not always have to initialize a variable
• Programming language may assign a default value
• Example
• int iStudentCount
• iStudentCount 456
• Alternative
• int iStudentCount 456

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Variable Content (contd.)

• Assigning a value to a character variable
• Enclose in single quotes
• Example
• char cMiddleInit
• cMiddleInit 'S'
• Alternative
• char cMiddleInit 'S'

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Variable Content (contd.)

• Assigning a value to a string variable
• Enclose in double quotes
• Example
• String sMiddleName "S" //Java
• string sMiddleName "S" //C

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Java and C Control Structuresand Program Flow

• Four types of control structures
• Invocation
• Top down
• Selection
• Repetition
• Correct use allows for a(n)
• Readable program
• Easy to maintain program

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Invocation

• The main() function block of code
• Tells operating system the starting point
• Function block of code performing a task
• Can return a value
• Example Save_Ferris.java file

public class Save_Ferris public static void
main(String args) System.out.println("I could
have been the Walrus!")
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Invocation (contd.)

• Parameters received value assigned to a variable
• Used by a block of source code
• Passing parameters as values
• Enter them on same line
• After Java program name
• Example C\gthello 10
• C has a main() function in every program
• Software engineers often include other files of
  source code to perform common task

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Invocation (contd.)

• C allows words inside parentheses
• Indicates parameters receiving data when the
  program runs
• Parameters allow users to pass data to main() and
  then use the data in the program
• Examples
• int argc, char argv
• //C main receiving parameters
• int main(int argc, char argv)

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Top Down (or Sequence)

• Used when program statements executed in
  sequential order
• Starting at the top and working down to the
  bottom
• See example code on pages 522 and 523

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Blocks of Code

• Sequence of several statements enclosed with
  opening and closing braces
• Indicates a relation
• Makes program more readable and accurate
• Braces are used most often when working with
  invocation, selection, repetition control
  structures
• Example

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Java Output Data

• Java System.out statement sends data to output
  device
• Insertion point where the cursor is placed
• Two methods to output data
• System.out.print(expression)
• System.out.println(expression)

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Java Output Data (contd.)
Table 15-10 Java output statements
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C Output Data

• C cout statement
• Sends data to output device
• Uses redirection symbols (ltlt) to direct output
• Example
• cout ltlt "15 10 " ltlt iResult ltltendl
• Instructs compiler to direct anything following
  the ltlt symbols to the defined output device

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C Output Data (contd.)
Table 15-11, Sample C output statements
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Input Data

• Java System.in
• Method to retrieve data from the input device
• Must create a new variable from the Scanner class
• Reads characters from input stream (keyboard)
• Places them into another variable acting as a
  memory buffer for storing the entered string
• Input assigned to a string variable declared by
  making a call to the next() method
• C cin
• Used to retrieve data from input device

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Back to Control Structures

• Java and C invocation
• Implemented by calling functions and methods
• Function performs a task, can return a value
• Method function belonging to a class
• Java equals() method
• System passes control to code associated with
  equals()
• Carries out the statements
• Makes the comparison
• Returns a Boolean value

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Selection

• First write algorithm with pseudocode
• Ensures program meets language requirements
• Guide or template for writing source code
• Recall Chapter 14 algorithm converting Celsius to
  Fahrenheit temperatures and vice versa
• See corresponding code on pages 531533

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if and if-else Statements

• Used to weigh results of decision making
• Result exists for every choice
• Syntax

if (condition) one or more statements
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if and if-else Statements (contd.)

• Condition
• Expression returning true or false value
• May add an else part to the control structure
• Performs a function if the if control structure
  evaluates to a false value
• Syntax

if (condition) one or more statements
else one or more statements
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if-else-if Statement

• Corrects problem in if-else statement
• User enters incorrect input value
• Allows certain blocks of code to execute
• Depends on variables state in the program while
  it is running
• Easy to use
• Makes program more flexible

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switch Statement

• Nesting
• Putting one control structure inside another
• Decreases codes readability
• switch statement
• Allows testing of many options
• Groups blocks of code to be executed depending on
  results
• Test expressions value
• Jump to some location in the switch statement
• Expression must be a scalar data type

41
switch Statement (contd.)
Copy editor Syntax alignment OK as is?
(different in PDF)

• break statement at end of each case
• Informs system to quit processing case statements
• Sends control to end of the switch statement
• Syntax

switch (expression) case value_1
statement_1 break case value_2
statement_2 break case value_3
statement_3 break default statement_4 break

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Repetition (Looping)

• Allows repeating statements multiple times
• No statement retyping
• Three statements
• for
• while
• do-while

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for Statement

• Used to repeat a group of statements a known
  number of times
• Variable declaration
• Declare and initialize a variable
• Declare counter variable
• Example int iCount
• Syntax

for (variable declaration expression
increment/decrement) statement(s)
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while Statement

• Processes a group of statements a certain number
  of times
• Like the for loop
• Precondition loop
• Loop checks the expression before any source code
  in the loop is executed
• Might never be executed
• Difference between for and while loops
• while statement doesnt provide a specified area
  for updating the counter

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while Statement (contd.)

• Syntax

while (expression) statements
46
do-while Statement

• Used when looping is based on an expression and
  statements are repeated before the expression is
  evaluated
• Mainly when processing a table
• Postcondition loop
• Executes at least one time before the expression
  is evaluated
• Syntax

do statement(s) while (expression)
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One Last Thought

• Most programming languages use the four major
  control structures discussed in this chapter
• Organizations select a programming language based
  on applications needs
• Programmers may need to update skills
• C and Java is a good start
• Must practice to become proficient
• Software engineers responsibility write
  easy-to-read and easy-to-maintain structured
  programs

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Summary

• Java high-level programming language designed
  for the Internet
• C high-level programming language based on the
  C language
• Incorporates object-oriented principles
• Variables
• Integer (int), character (char), floating point,
  Boolean, and string
• Initializing a variable assigning a value to a
  variable

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Summary (contd.)

• Four high-level programming language control
  structures
• Invocation, top down, selection, repetition
• Java uses methods for the invocation
• C uses methods and functions
• Output data
• Java uses the System.out statement
• C use the cout statement with the ltlt
  redirection symbols

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Summary (contd.)

• Input data
• Java Scanner class gathers input
• C uses the cin statement
• Selection control structures
• C and Java use if, if-else, if-else-if, switch
• switch statement is used only with scalar
  variables
• Repetition
• C and Java use for, while, do-while loops
• Practice, practice, and more practice