1 © 2002 John Urrutia. All rights reserved. Qbasic Constructing Qbasic Programs

2 © 2002 John Urrutia. All rights reserved. Program Development Problem definition – statement  Who – The person, group, organization  What – The record, file, system, data  When – The timeframe  Where – The location  Why – The business reason

3 © 2002 John Urrutia. All rights reserved. Steps in Program Development 1. Clearly State the Problem  Data  Input – what are the data sources.  Output – what are the data sinks.  Process (algorithm)  Detailed description of how the Input is manipulated into Output.

4 © 2002 John Urrutia. All rights reserved. Data decomposition – the process of:  Identifying the required output.  Reports  Files  Identifying the raw input data needed to find a solution.  Can be an elementary data element  Can be a grouped data element Steps in Program Development

5 © 2002 John Urrutia. All rights reserved. The Algorithm – is the process  Sequence – linear execution of instructions  Selection – Identify a processing path  Binary  Case  Iteration – repetitive execution of instructions Steps in Program Development

6 © 2002 John Urrutia. All rights reserved. Steps in Program Development 2. Plan the Logic of the program  Use one or more of these to graphically represent the algorithm.  Flowchart  Pseudocode  Hierarchy chart

7 © 2002 John Urrutia. All rights reserved. Flowcharts  A graphical representation of the problem definition Process Decision Termination Manual Screen Steps in Program Development

8 © 2002 John Urrutia. All rights reserved. Hierarchy charts (Visual TOC)  A graphical representation of the functional decomposition Steps in Program Development Room Area Program Room Area Program Room Area Program Room Area Program

9 © 2002 John Urrutia. All rights reserved. Steps in Program Development Pseudocode  An English-like representation of the problem definition  IF the meat is green THEN move it to the waste bucket ELSE move it to the good bucket.

10 © 2002 John Urrutia. All rights reserved. Steps in Program Development 3. Code the program The syntactical exercise of converting the program design into a specific programming language. This should be done first on paper.

11 © 2002 John Urrutia. All rights reserved. Steps in Program Development 4. Key the program. Transfer the coded program into the QBASIC environment and save it as a QBASIC file.  MyProg.bas

12 © 2002 John Urrutia. All rights reserved. Steps in Program Development 5. Test and Debug the program.  V&V –Verification & Validation  Verification – Are we doing the right job?  Validation – Are we doing the job right?

13 © 2002 John Urrutia. All rights reserved. Steps in Program Development Specification errors –  Problem definition omissions, inaccuracies, lack of clarity Syntax errors –  Coding or Keying Logic errors  Do what I think not what I say…

14 © 2002 John Urrutia. All rights reserved. Steps in Program Development 6. Complete the Documentation  Develop a program package containing:  Program specification, hierarchy chart, flowchart, and pseudocode.  Test plan and results  Final version of tested program

15 © 2002 John Urrutia. All rights reserved. B. A. S. I. C. Beginners All-purpose Symbolic Instruction Code QBasic – QuickBASIC  Developed at Dartmouth in 1960’s

16 © 2002 John Urrutia. All rights reserved. Qbasic Character Set Letters: a-z and A-Z Digits: 0-9 Blank: the space character ( ) Special characters: + - * / \ =., ’ ” ( ) : ; ^ _ $ # ? ! % &

17 © 2002 John Urrutia. All rights reserved. Qbasic Keywords A keyword has a predefined meaning within Qbasic.  Examples: LET END REM PRINT

18 © 2002 John Urrutia. All rights reserved. The QBASIC Environment QBASIC is an interpreter  Each line of code is translated into machine language just prior to its execution… every time.  Creates an interactive environment that’s easy to work with.

19 © 2002 John Urrutia. All rights reserved. QBASIC …

20 © 2002 John Urrutia. All rights reserved. Demonstration

21 © 2002 John Urrutia. All rights reserved. The CLS statement CLear Screen  Erases all characters from the terminal  Places cursor at position 1,1 (top left corner)

22 © 2002 John Urrutia. All rights reserved. The PRINT statement Writes information to the terminal. PRINT output-list PRINT X$ PRINT PRINT “Hello World” PRINT (prints a blank line)

23 © 2002 John Urrutia. All rights reserved. The PRINT statement Horizontal spacing  Each PRINT statement will occupy one line on the users screen Vertical spacing  ; – places data adjacent to each other , – places data at multiples of 14 columns on the line