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QBASIC

QBASIC. Chapter 2 Modular Programs with Calculations and Strings. QBASIC Character Set. Letters: a-z and A-Z Digits: 0-9 Blank: the space character ( ) Special characters: + - * / = < > . , ’ ” ( ) : ; ^ _ $ # ? ! % &. Qbasic Keywords.

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QBASIC

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  1. QBASIC Chapter 2 Modular Programs with Calculations and Strings

  2. QBASIC Character Set • Letters:a-z and A-Z • Digits:0-9 • Blank:the space character ( ) • Special characters:+ - * / \ = < > . , ’ ” ( ) : ; ^ _ $ # ? ! % &

  3. Qbasic Keywords • A keyword has a predefined meaning within Qbasic. • Examples:LET END REM PRINT

  4. Constants & Variables • Constants • “literal” values that cannot be changed • May or may not have a label • Variables • Value can be changed • Must be referenced by a label

  5. QBASIC Constants • Numeric Constants • Can only contain these 13 characters: + - . 0 1 2 3 4 5 6 7 8 9 • If not identified with a label they are called a “literal” • Can not have + - internal or trailing • Can only have one decimal

  6. Numeric Constants 123+234-456+123.456.678amount = 345678.1234567

  7. Labels • A name assigned to represent a variable. • Must start with a letter • Should be meaningful. • Can have periods imbedded. • Should carry the data type.

  8. The LET statement • Assigns a value to a variable.Can be Explicit or Implicit LET variable.Name = value LET my.nbr! = 0 LET my.str$ = “This is my string” LET tot! = tot! + purchases! + taxes!

  9. QBASIC Data Types • All data in QBASIC is identified by a data type • Numbers • % – Integer -32,768 to 32,767 • & – Long integer -2,147,483,648 to 2,147,483,647 • ! – Single precision 7 digit (1038 )(Default data type) • # – Double precision 15 digit (10308 )

  10. QBASIC Data Types • Strings: • $ - data type identifier • Any set of characters enclosed in double quotation marks. • “ ” • Maximum of 14,656 Characters

  11. Arithmetic Operators • * – Multiplication • ^ – Exponentiation • / – Division • \ – Integer Division • MOD – Modula (remainder) • + – Addition • - – Subtraction

  12. Calculations • Order of operations (precedence) • ^ (Power) • +, - (Unary) • *, /, \, MOD, +, - (Arithmetic) • <, <=, >, >=, <>, = (Relational) • Boolean operators • NOT, AND, OR, XOR, EQV, IMP

  13. Some math Examples LET A% = 100LET B% = 4PRINT A% * B% PRINT A% + B% - B% * 4 MOD 3 400 PRINT A% + B% - B% * (4 MOD 3) 103 100

  14. Functions • A function is a set of instructions that perform a specific task. • FunctionName (argument1, …) • Built-in & User defined X$ = INT(X)

  15. Built-in Functions • Conversions • MKI$ - CVI, MKD$ - CVD • CHR$ - ASC • CINT(), CSGN(), CDBL() • System • DATE$ - TIME$

  16. The INPUT statement • INPUT variable-listINPUT “prompt ” ; or , variable-list • prompt – any valid string • ; – Question mark generated • , – No Question mark generated • variable-list – mix and match separate with commas

  17. Using INPUT to prompt users INPUT “Want a date”; date.in Want a date?__ INPUT “Enter date”, date.inEnter date __

  18. Modular Programming • As we have seen previously: • Heirarchy Charts allow us to break large problems into smaller more manageable blocks that perform a specific unit of work • Each of these “blocks” can be represented as a “subroutine”. A fixed combination of instructions that can be re-used.

  19. Subroutines • A subroutine is identified with a label just like variables. • Subroutines are “called” from someplace in the program using GOSUB and return to the statement following the call using the RETURN statement.

  20. GOSUB label.name GOSUB my.summationPRINT “The sum is “; x%END my.summation: INPUT “Number Please:”, y% x%=(y-1)+(y-2)+(y-3)… RETURN

  21. RETURN [label.name] • Returns to caller by default • Command following the GOSUB gets control • Returns to label if specified • Should only be used under special circumstances.

  22. Hierarchy Chart ScoreAverageProgram InputName & Scores CalculateAverage OutputName &Average

  23. Start InputScores CalculateAverage WriteOutput Inputname & scores InputName Avg1 = (3 Scores)/3 PrintName &Average Input 3Scores Return CalculateAverage Average = Avg1 Round Return OutputName &Average Return End Flowchart Start InputScores CalculateAverage WriteOutput Inputname & scores InputName Avg1 = (3 Scores)/3 PrintName &Average Input 3Scores Return CalculateAverage Average = Avg1 Round Return OutputName &Average Return End

  24. Code MAIN:GOSUB Input.Name.ScoresGOSUB Calculate.AverageGOSUB Write.Output END.MAIN:END Input.Name.Scores:INPUT “Enter Name: “ , Name$INPUT “Enter Score 1: “ , Score1%INPUT “Enter Score 2: “ , Score2%INPUT “Enter Score 3: “ , Score3%RETURN Calculate.Average: Avg=INT((Score1%+ Score2%+ Score3%)/3)):RETURN Write.Output: PRINT Name$; ” – “; Avg: RETURN

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