Module 10: Computer Programming

computer program (application)

• step-by-step instructions that tells the computer what to do. 

  • A program is written by computer programmers using a programming language. 

Software engineering

• uses mathematical, engineering and management techniques to reduce the cost and complexity of a program while increasing its reliability and modifiability.

Programmers typically specialize in either application programming or systems programming:

•  Application programmers

•  Systems programmers 

 Application programmers

•  create business and productivity applications, mobile apps, web apps and games.

Systems programmers 

• develop systems software such as operating systems, device drivers, security modules and communications software.

Two approaches used in program development are

• procedural (also called structured) programming

• object-oriented programming.

Procedural programming

•  is used when a program can be created with step-by-step instructions (called an algorithm) that are performed in a sequential manner. 

  • Each programming task is performed using separate chunks of code called procedures or modules.

Object-oriented programming 

• focuses on the objects that make up the program and how these objects interact with one another. 

  • Each object contains attributes (also called properties) that describe the object and methods that are tasks related to objects.

The fundamental concepts behind object-oriented programming are:

•  Objects 

• Attributes

• Method

• Message

• Class

Objects

• a person, place, or thing within the program (employee, pizza, GUI button)

Attributes

•  a characteristic of an object (employee name, pizza diameter, button color)

Method

• statements that define an action performed by an object or to an object (hire an employee, sell a pizza, click on a button)

Message

• A line of code that "calls" or directs the program to perform a specific method

Class

• a group of objects that share common attributes (employees, menu items, GUI controls)

Companies have used object-oriented programming languages for new program development since the mid-1990s.

• Popular object-oriented programming languages are Java, Python and C++.

Software development life cycle. 

• The five-step process that most programmers follow when creating a program development life

  • The five steps (or phases) are illustrated on the next page.

Phase 1: Requirements Analysis

•  What does the application need to do?

•  When does it have to be completed?

•  What programming language will be used?

•  How the program will interact with other programs in the organization

•  What documentation is required (program code, pseudocode, program flowcharts, UML diagrams, class diagrams, test results, user manual)

Phase 2: Design

• In the design phase the programmer designs the algorithm that the program will perform, using design tools such as pseudocode, program flowcharts, use case diagrams and class diagrams.

Pseudocode

• uses short statements to explain the sequence of steps involved in a program

Program flowcharts

• use geometric shapes, lines and arrows to show the sequence of steps in a program

 Unified Modeling Language (UML)

• used for modeling object-oriented programs

Two UML modeling tools are use case diagrams and class diagrams:

• A use-case diagram documents the users of a program and the functions they perform

•  A class diagram lists the attributes and methods of the objects in a program

Sequence

• the programming statements follow one after another in sequential order.

Selection

• the programming statements that will be performed next depends upon whether a certain condition is true or false (has a bill been paid? is a library book overdue?)

Repetition (also called loop or iteration)

• a block of programming statements repeats until a certain condition is met (calculate invoices until all customer orders have been processed)

Phase 3: Development (Coding)

• Program development is when a programmer converts the program design (flowchart, class diagram, etc.) into a functioning program using a programming language.

 Every programming language has its own syntax

•  Every programming language has its own syntax, which is the combination of rules, punctuation, capitalization and keywords that the program must follow.

Variables

• one or more characters that represent the value of a data item within a program 

  • (FirstName, PhoneNum, PayRate). 

  • The value of a variable can change throughout a program.

Keywords

• words that a programming language has reserved for a specific function. 

  • Keywords cannot be used as variables.

Comments (remarks):

• Text information placed within a program to explain the purpose of the programming code immediately following the comment.

Comment lines

• begin with special characters (such as forward slashes, apostrophes or asterisks). 

  • are necessary to help programmers understand what the program is doing next. 

The type of characters used to indicate a comment

• depends upon the programming language being used. 

The special character(s)

• indicate that the line is a comment line and NOT part of the programming code. 

In the development phase programmers decide

• what variables and control structures they will use, code the program using the keywords and syntax of the programming language,

• type comments within the programming code.

Agile development methodology:

• When the requirements of a program are not easily defined and/or

  •  A goal is allowing users to participate in the development process and an agile methodology is used.

• focuses on breaking the overall application into smaller, functional pieces of code. 

  • Each piece of code is treated like a separate software project of its own.

•  Users test each piece of code separately and provide feedback concerning how they want the code modified

•  The code, test, and feedback process can have multiple iterations (called sprints) until the user is completely satisfied with that piece of code.

•  Sometimes the small pieces of code are implemented as soon as they are completed--while other pieces of code related to the larger application are still being coded, tested and modified

The programming language that will be used to create a program is determined

• in the requirements analysis phase of the SDLC. 

  • However, the development phase is when a programmer begins typing the programming code using an integrated development environment (IDE).

Integrated development environment (IDE). 

•  is a software package that provides tools to type and edit programming statements, automate and simplify parts of the coding process, debug errors and compile and run the program. 

  • Every programming language has its own specific IDE. 

Phase 4: Program Testing & Debugging

In this phase programmers “run” the program by sending the program to a language translator. 

• A language translator 

  • converts a programming language (called source code) into the 0's and 1's of a machine language (called object code). 

    • A computer can only run the object code of a program. 

    • In this phase programmers also fix (debug) programming errors. 

There are two main types of language translators:

• compilers

• interpreters.

compiler

•  converts the entire application into object code before sending it to the CPU for processing. 

  • Compilers are unique for each programming language.

 interpreter

•  similar to a compiler, except that it translates and executes programming code one line at a time as the program is being run.

There are three types of programming errors:

• runtime errors,

• syntax errors

• logic errors.

 Runtime errors are

• when a line of code cannot be executed. 

  • For example, attempting to divide by zero, multiply by a variable that is not a number

 Syntax errors

• occur when the programmer has not followed the rules or grammar of the programming language. 

  • Examples of syntax errors are misspelled words, incorrect punctuation, incorrect capitalization, not defining variables, etc. 

  • Syntax errors prevent the program from finishing, so they must be fixed before the program will produce a result. 

• Syntax errors are normally detected and identified by the compiler.

Logic errors occur

•  when the program contains no runtime or syntax errors, but produces incorrect results. 

•  are caused by incorrect programming “logic” such as using a wrong mathematical formula or putting coding statements in the wrong sequence. 

  • Because compilers cannot identify logic errors, they are often much more difficult to find and fix than runtime or syntax errors.

Programmers debug programs in one of three ways:

•  Compilers identify the statement where runtime and syntax errors have occurred and often even explain the reason for the error

•  Debugging tools step through a program and monitor the status of variables, input and output. 

  • Debugging tools can be packaged with a programming language or can be obtained as an add-on

•  Programmers can read through each line of code and proofread for incorrect statements

To verify the program will provide correct results no matter what type of data the user enters: 

• programmers test a program with both valid and invalid (negative numbers, numbers that exceed the variable maximum value, wrong data types) data. 

• The program should provide clear error messages when invalid data is entered by the user.

Beta testing

•  is when a software company provides free review copies of a new program to selected companies. 

• The companies are asked to use the program and report back to the vendor any programming bugs. 

• In exchange for their help, the testing companies are either given a free or discounted copy of the final product when it is released to the public.

Once a program has been tested and debugged, the programmer should complete the program documentation and develop user documentation:

•  Program documentation 

•  User documentation explains how to use the program. 

Program documentation

• explains how the program is designed (using tools such as flowcharts, pseudocode and class diagrams) 

• provides comments within the programming statements that explain what the next few lines of code will accomplish.

 User documentation explains how to use the program.

• These instructions can be accessed by a help button on the program's user interface or are provided in a user manual

Phase 5: Program Maintenance

•  until the organization decides that it needs a completely new application. 

  • At that point the company uses the SDLC methodology once again to create a new application.

•  That is why this methodology is called a life cycle. 

• A program is created, is used for several years, and is eventually replaced by a new program.