1 © 2000 John Urrutia. All rights reserved. Qbasic Looping Statements & Formatted Output.

1© 2000 John Urrutia. All rights reserved.

Qbasic

Looping Statements&

Formatted Output


Here we go Loop de LoopA loop is a set of statements that are

executed repeatedly.

Types Controlled

Pre-testPost-test

Infinite


Infinite LoopsGenerally a bad thing.

Keeps going and going and …

Going Going GoingGoing Going GoingGoing Going Going


Controlled LoopsGoverned by a condition.

LogicalSentinel

MathematicalCounter

EnvironmentalEOF()


Infinite

DO…LOOP syntax

DO

statements

LOOP

Pre-Test

{ WHILE | UNTIL }

condition

{ WHILE | UNTIL }

condition

Post-Test


ConditionA comparison of two or more things.

The comparison will result in: TRUE state

FALSE state


DO WHILE…LOOP StatementPretest loop

If condition is true execute

DO WHILE DAY$ = YES$

PRINT “Is it Night yet?”

LOOP


DO…LOOP UNTIL StatementPosttest loop

Executes at least once

DO

PRINT “DO-WAH-DIDDY”

LOOP UNTIL The.Cows = Come.Home


Boolean or Logical Expressions

Used in all conditions

Algebra created by George Boole

Always evaluates to a binary stateGenerally:

1 is TRUE0 is FALSE


Relational ExpressionsSingle relational operator two operands

< Less than

> Greater than

= Equal to

<= Less than or equal to

>= Greater than or equal to

<> Not equal to


ComparisonsNumeric comparisons are simple.

Compares bit for bit

Negative numbers are stored in 2’s compliment+110 = 000016 = 0000 0000 000 000012

+010 = 000016 = 0000 0000 0000 00002

-110 = FFFF16 = 1111 1111 1111 11112

-210 = FFFE16 = 1111 1111 1111 11102

-310 = FFFD16 = 1111 1111 1111 11012


ComparisonsStrings are based on the collating

sequence (ASCII shown below)“1”char =4810 =3016 =0011 00002

“9”char =5710 =3916 =0011 10012

“A”char =6510 =4116 =0100 00012

“Z”char =9010 =5A16 =0101 10102

“a”char =9710 =6116 =0110 00012

“z”char =12210 =7A16 =0111 10102


When is an “A” not an “a”?When comparing strings the case

counts.Use the UCASE$() function to limit the

number of options from your user.


Compound ConditionsWhen 2 or more expressions are

combined together.

Used to specify complex conditions in one statement.


Boolean OperatorsNOT – negation (bit-wise complement)

AND – logical addition (conjunction)

OR – logical subtraction (disjunction)

XOR – exclusive “or”

EQV – logical equivalence

IMP – logical implication


NOT Boolean Truth Tables

Expr NOT

FalseTrue

False True


AND Boolean Truth Tables

Expr 1 Expr 2 AND

True True True

FalseTrue False

False True False

False False False


OR Boolean Truth Tables

True True True

FalseTrue True

False True True

False False False

Expr 1 Expr 2 OR


Nested LoopsA loop within a loop

ones% = 0tens% = 0DO WHILE tens% < 10 DO WHILE ones% < 10

PRINT tens% ; “-“ ; ones% ones% = ones% + 1

LOOPones% = 0tens% = tens% + 1

LOOP


More Formatted OutputTAB(n)

n – represents the column number to tab to

SPC(n) n – represents the number of spaces to insert


TAB examples

PRINT TAB(10); “10”; TAB(20); “20”; TAB(30); “30”

00000000011111111112222222222333333333341234567890123456789012345678901234567890

10 20 30


SPC example

PRINT SPC(10); “10”; SPC(10); “20”; SPC(10); “30”

00000000011111111112222222222333333333341234567890123456789012345678901234567890

10 20 30


The PRINT USING statementWrites formatted data to the teminal

PRINT USING “format-string” ; output-list

The format-string specifiesNumeric edited data formats

String formats

Literal data


USING format charactersStrings

\n\ – first n +2 characters in the string

! – first character in the string

& – no formatting

_ – print character not format


USING format charactersNumbers

# – number digit

. – decimal point

, – thousands separator

+ – sign of number

- – trailing minus sign

$ $$ – fixed / floating dollar sign


PRINT USING exampleSPRINT USING “A=# and B=$#,###.##”; 5; 1234.56

A=5 and B=$1,234.56

PRINT USING “You’re a \ \ and I’m a & _!”; “nutria”; “foolish”

You’re a nut and I’m a fool!


Qbasicscreen manipulation

The LOCATE statement


LOCATELOCATE – position on screen

row% , column%

cursor%

start%

stop%

CSRLIN – line cursor is on

POS(0) – column cursor is on

1 © 2000 John Urrutia. All rights reserved. Qbasic Looping Statements & Formatted Output.

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