Introduction to HighLevel Language Programming

1
Chapter 8

• Introduction to High-Level Language Programming

2
Objectives

• In this chapter, you will learn about
• Where do we stand?
• High-level languages
• Introduction to C
• Virtual data storage
• Statement types
• Putting the pieces together

3
Objectives Postponed(Covered in CS23021)

• Functions
• Managing complexity
• Object-oriented programming
• Graphical programming
• The big picture Software engineering

4
Where Do We Stand?

• Early days of computing
• Programmers used assembly language
• Programs written by technically oriented people
• Assembler programs
• Were machine specific
• Required programmers take a microscopic view of a
  task
• Later decades
• Programmers demanded a more comfortable
  programming environment
• Programs could be written by nontechie people
• Programs could be portable rather than machine
  specific
• Programmers could avoid data storage and movement
  issues

5
High-level Languages

• High-level programming languages
• Called third-generation languages
• Machine language was first generation
• Assembly language was second generation
• Overcame deficiencies of assembly language
• Programmer didnt need to manage details of data
  storage or movement

6
High-level Languages (continued)

• Expectations of a high-level language program
  (continued)
• Programmer can take a macroscopic view of tasks
  primitive operations can be larger
• Program will be portable
• Code will be closer to standard English and use
  standard mathematical notation

7

• Figure 8.1
• Transitions of a High-level Language Program

8
Introduction to C

• Some components of program on next slide
• Comments
• Anything following // on a line is a comment
• Give information to human readers of code
• The include directive
• The linker includes object code from a library
• C does not provide input or output of data
  (I/O)
• The using directive
• Tells compiler to look in a namespace for
  definitions not mentioned in the program
• Used here for I/O commands cin cout
• Main program code in brackets after main

9

• A Simple C Program

Figure 8.2
10

• Figure 8.3
• The Overall Form of a Typical C Program

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Data Types

• Identifiers Names in a programming language
• Any combination of letters, digits, and
  underscore symbol that does not start with a
  digit.
• Should select names suggestive of meaning
• Keywords Have special meanings in C
• Also called reserved words.
• Can not be used as an identifier
• C is a case-sensitive, free-format language
• Data items can be constants or variables

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Data Types (continued)

• A declaration of a data item tells
• Whether the item is a constant or a variable
• The identifier used to name the item
• The data type of the item

13

• Figure 8.5
• Some of the C Standard Data Types

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Data Types (continued)

• An array
• Groups together a collection of memory locations,
  all storing data of the same type
• Example
• Int Hits12

Figure 8.6 A 12-Element Array Hits
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Statement Types

• Input/output statements
• Input statement
• Collects a specific value from the user for a
  variable within the program
• Output statement
• Writes a message or the value of a program
  variable to the users screen or to a file

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Statement Types (continued)

• Assignment statement
• Assigns a value to a program variable
• Control statement
• Directs the flow of control
• Can cause it to deviate from usual sequential flow

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Input/Output Statements

• Example
• Pseudocode
• Get value for Radius (interactively from
  keyboard)
• C
• cin gtgt Radius
• cin Input stream
• Code for extraction operator (gtgt) and the
  definition of the cin stream come from the
  iostream library and std namespace

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Input/Output Statements (continued)

• Example
• Pseudocode
• Print the value of Circumference (on screen)
• C
• cout ltlt Circumference
• cout Output stream
• Code for the insertion operator (ltlt) and the
  definition of the cout stream come from the
  iostream library and std namespace

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Input/Output (cont.)

• Consider real numbers such as 84.8232
• The fixed format output of this number would be
• 84.8232
• In scientific notation, this output would be
• 8.48232e001
• The computer is free to choose the output style.
• To specify fixed format output, include the
  following formatting statement in the program
• cout.setf(iosfixed)
• To require the output be in scientific notation,
  use
• cout.setf(iosscientific)
• To require two decimal places, use
• cout.precision(2)

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Output using literal strings

• Suppose we want to output message before the
  value, such as
• The circumference that corresponds to this
• radius is 84.8234
• This could be accomplished using
• cout ltlt The concumference that corresponds
• ltlt to this radius is ltlt Circumference
• Many other output features are available
• Some additional information is given in textbook
• We wont cover the output options in detail here.

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The Assignment Statement

• General form
• Pseudocode
• Set the value of variable to arithmetic
  expression
• C assignment statement evaluation
• variable expression
• Expression on the right is evaluated
• The result is written into the memory location
  specified on the left
• Example Consider assemby code for
• A B C - 3

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Assignment Statements (cont.)

• The C symbols for four basic operations
• Addition
• - Subtraction
• Multiplication
• / Division
• Example The product of A B is AB.
• Data Type Considerations
• If A and B are integers, then A/B is the integer
  obtained by truncation 7/2 is 3
• If either A or B is a real number then A/B is a
  real number 7/2 is 3.5
• Other data-type considerations are covered in
  textbook, and will be used, as needed.

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Control Statements

• Types of control mechanisms
• Sequential
• Instructions are executed in order
• Conditional
• Choice of which instructions to execute next
  depends on some condition
• Looping
• Group of instructions may be executed many times

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Control Statements (continued)

• Sequential is the default mode of execution
• Conditional flow of control
• Evaluation of a Boolean condition (also called a
  Boolean expression)
• Which programming statement to execute next is
  based on the value of the Boolean condition (true
  or false)

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Control Statements (continued)

• Conditional flow of control (continued)
• if-else statement
• if (Boolean condition)
• S1
• else
• S2
• if variation of the if-else statement
• if (Boolean condition)
• S1

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• Figure 8.10
• Conditional Flow of Control (flowchart)
• (If-Else)

27

• Figure 8.11
• If-Else with Empty Else

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Control Statements (continued)

• Looping (iteration)
• The loop body may be executed repeatedly based on
  the value of the Boolean condition
• while statement
• while (Boolean condition)
• S1

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• Figure 8.12
• While Loop

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Putting the Pieces Together

• At this point, we can
• Perform input and output
• Assign values to variables
• Direct the flow of control using conditional
  statements or looping
• For a complete program, we need to
• Assemble the statements in the correct order
• Fill in the missing pieces

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Meeting Expectations

• C meets the four expectations for a high-level
  programming language
• Expectations
• A programmer need not manage the details of the
  movement of data items within memory, nor pay any
  attention to where they are stored

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Meeting Expectations

• Expectations (continued)
• Programmer can take a macroscopic view of tasks,
  thinking at a higher level of problem solving
• Programs written in high-level languages will be
  portable rather than machine-specific
• Programming statements in a high-level language
• Will be closer to standard English
• Will use standard mathematical notation

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Pseudocode Language Instructions in C(Sections
8.1 8.6)

• Recall pseudocode language instructions (pg 58)
• Computation
• Set value of variable to arithemetic
  expression
• Input/Output
• Get a value for variable
• Print the value for variable
• Print the message message
• Conditional
• If a boolean expression is true then
• First set of algorithmic operations
• Else
• Second set of algorithmic operations

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Pseudocode Language Instructions (cont.)

• Iteration (looping)
• While (a boolean condition is true) do
• operation
• operation
• .....
• operation
• End of Loop

35
Computation Expressions in C
An expression in C is a sequence of operators
and operands which adhere to the C syntax
rules. The operators are grouped according to an
order of precedence, and associativity
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Computation Expressions in C

• Example 1 a b c d
• Example 2 a b c d e
• Example 3 a (b c) (d-e)
• Example 4 a b / c
• Example 5 a b c
• Example 6 a b c d
• Other , -, , /, ???

Assume b 5, c 3, d 4, e 2
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Computation (cont.)

• Consider equation ax2 bx c 0
• The roots are x ( b ? sqrt(b2 4ac) ) / 2a
• Using a high level language we could write
• discrim bb 4ac
• root1 (-b sqrt(discrim)) / (2a)
• root2 (-b sqrt(discrim)) / (2a)
• This closely resembles the way we look at the
  problemmathematically

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Input and Output in C

• /
• circle03.cpp
• Gets the radius of a circle,
  calculatesits circumference and prints out the
  result
• /
• include ltiostreamgt
• using stdcin
• using stdcout
• int main()
• const double PI 3.14159
• double radius 0.0, circumference 0.0
• cout ltlt "Please enter the radius " ltlt '\n'
• cin gtgt radius
• circumference 2 PI radius
• cout ltlt The circumference is

• i/o example 3
• cout prompt user for data
• ltlt (insertion operator)
• cin store data in a variable
• gtgt (extraction operator)
• cout output data entered

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Conditional Statements in C

• Conditional flow of control (continued)
• if-else statement
• if (Boolean condition)
• S1
• else
• S2
• if variation of the if-else statement
• if (Boolean condition)
• S1

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• Figure 8.12
• Conditional Flow of Control
• (If-Else)

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• Figure 8.13
• If-Else with Empty Else

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Iterative Statement in C

• Looping (iteration)
• The loop body may be executed repeatedly based on
  the value of the Boolean condition
• while statement
• while (Boolean condition)
• S1

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• Figure 8.14
• While Loop

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Interative Example in C

• Sum 0 //initialize Sum
• cout ltlt Please enter the numbers to add
• cout ltlt terminate with a negative number. ltlt
  endl
• cin gtgt Number // this will get the first
  value
• while (Number gt 0)
• Sum Sum Number
• cin gtgt Number
• cout ltlt The total is ltlt Sum ltlt endl

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Summary

• In a high-level language, the programmer
• Need not manage storage
• Can think about the problem at a higher level
• Can use more powerful and more natural-language-li
  ke program instructions
• Can write a much more portable program