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

2 © 2000 John Urrutia. All rights reserved. Here we go Loop de Loop A loop is a set of statements that are executed repeatedly. Types  Controlled  Pre-test  Post-test  Infinite

3 © 2000 John Urrutia. All rights reserved. Infinite Loops Generally a bad thing. Keeps going and going and … Going

4 © 2000 John Urrutia. All rights reserved. Controlled Loops Governed by a condition.  Logical  Sentinel  Mathematical  Counter  Environmental  EOF()

5 © 2000 John Urrutia. All rights reserved. Infinite DO…LOOP syntax DO statements LOOP Pre-Test { WHILE | UNTIL } condition Post-Test

6 © 2000 John Urrutia. All rights reserved. Condition A comparison of two or more things. The comparison will result in:  TRUE state  FALSE state

7 © 2000 John Urrutia. All rights reserved. DO WHILE…LOOP Statement Pretest loop  If condition is true execute DO WHILE DAY$ = YES$ PRINT “Is it Night yet?” LOOP

8 © 2000 John Urrutia. All rights reserved. DO…LOOP UNTIL Statement Posttest loop  Executes at least once DO PRINT “DO-WAH-DIDDY” LOOP UNTIL The.Cows = Come.Home

9 © 2000 John Urrutia. All rights reserved. Boolean or Logical Expressions Used in all conditions Algebra created by George Boole Always evaluates to a binary state  Generally:  1 is TRUE  0 is FALSE

10 © 2000 John Urrutia. All rights reserved. Relational Expressions Single relational operator two operands  <Less than  >Greater than  =Equal to  <=Less than or equal to  >=Greater than or equal to  <>Not equal to

11 © 2000 John Urrutia. All rights reserved. Comparisons Numeric comparisons are simple.  Compares bit for bit  Negative numbers are stored in 2’s compliment  = =  = =  = FFFF 16 =  = FFFE 16 =  = FFFD 16 =

12 © 2000 John Urrutia. All rights reserved. Comparisons Strings are based on the collating sequence (ASCII shown below)  “1” char =48 10 =30 16 =  “9” char =57 10 =39 16 =  “A” char =65 10 =41 16 =  “Z” char =90 10 =5A 16 =  “a” char =97 10 =61 16 =  “z” char = =7A 16 =

13 © 2000 John Urrutia. All rights reserved. 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.

14 © 2000 John Urrutia. All rights reserved. Compound Conditions When 2 or more expressions are combined together. Used to specify complex conditions in one statement.

15 © 2000 John Urrutia. All rights reserved. Boolean Operators NOT– negation (bit-wise complement) AND– logical addition (conjunction) OR– logical subtraction (disjunction) XOR– exclusive “or” EQV– logical equivalence IMP– logical implication

16 © 2000 John Urrutia. All rights reserved. NOT Boolean Truth Tables Expr NOT FalseTrue FalseTrue

17 © 2000 John Urrutia. All rights reserved. AND Boolean Truth Tables Expr 1Expr 2 AND True FalseTrue False TrueFalse

18 © 2000 John Urrutia. All rights reserved. OR Boolean Truth Tables True FalseTrue FalseTrue False Expr 1Expr 2 OR

19 © 2000 John Urrutia. All rights reserved. Nested Loops A loop within a loop ones% = 0 tens% = 0 DO WHILE tens% < 10 DO WHILE ones% < 10 PRINT tens% ; “-“ ; ones% ones% = ones% + 1 LOOP ones% = 0 tens% = tens% + 1 LOOP

20 © 2000 John Urrutia. All rights reserved. More Formatted Output TAB( n )  n – represents the column number to tab to SPC( n )  n – represents the number of spaces to insert

21 © 2000 John Urrutia. All rights reserved. TAB examples PRINT TAB(10); “10”; TAB(20); “20”; TAB(30); “30”

22 © 2000 John Urrutia. All rights reserved. SPC example PRINT SPC(10); “10”; SPC(10); “20”; SPC(10); “30”

23 © 2000 John Urrutia. All rights reserved. The PRINT USING statement Writes formatted data to the teminal PRINT USING “ format-string ” ; output-list The format-string specifies  Numeric edited data formats  String formats  Literal data

24 © 2000 John Urrutia. All rights reserved. USING format characters Strings  \n\ – first n +2 characters in the string  ! – first character in the string  & – no formatting  _ – print character not format

25 © 2000 John Urrutia. All rights reserved. USING format characters Numbers  # – number digit . – decimal point , – thousands separator  + – sign of number  - – trailing minus sign  $ $$ – fixed / floating dollar sign

26 © 2000 John Urrutia. All rights reserved. PRINT USING example S PRINT USING “A=# and B=$#,###.##”; 5; A=5 and B=$1, PRINT USING “You’re a \ \ and I’m a & _!”; “nutria”; “foolish” You’re a nut and I’m a fool!

27 © 2000 John Urrutia. All rights reserved. Qbasic screen manipulation The LOCATE statement

28 © 2000 John Urrutia. All rights reserved. LOCATE LOCATE – position on screen  row%, column%  cursor%  start%  stop% CSRLIN – line cursor is on POS(0) – column cursor is on