Basic Programming

1
Basic Programming

• Joe Komar

2
Computer Programs
Processing
Input
Output
3
Programming Tools

• Flowcharts
• Pseudocode
• Top-down Charts

4
Flowcharts
Flowline
Input/Output
Terminal (start/end)
Decision
Processing
5
Flowcharts
Start
Read Data
Process Data
Print Result
End
6
Pseudocode

• English like description of program steps
• Read number of items and cost
• Multiply cost times number
• Display the number of items, cost, and total

7
Top-Down Chart
Program Name
Process Data
Output Results
Read Input Data
8
Programming Structures

• Sequential -- One step after another
• Decision Structure -- IF...Then...Else
• Looping Structure -- DO WHILE (or DO UNTIL)

9
Sequential Structure
Step 1
Step 2
Step 3
10
Decision Structure
Then
Else
IF
Process 2
Process 1
11
Looping Structure
NO
True?
YES
Process
12
Arithmetic Operations

• Addition
• Subtraction -
• Multiplication
• Division /
• Exponentiation

13
Numbers

• Constants -- e.g. 17, 1.329, 1.4E3
• Variables -- Names for areas in memory that can
  have different values at different times
• Up to 40 characters
• Must begin with a letter of the alphabet
• Only letters, digits, and periods
• Smallest is one letter

14
Sample Program

• CLS
• LET rate 50
• LET time 14
• LET distance rate time
• PRINT distance
• LET distance 410
• LET time distance / rate
• PRINT time
• END

15
Basic Statements

• CLS -- Clears Screen
• LET -- LET var expression
• PRINT -- PRINT list (use of )
• END -- signifies end of program

16
Qbasic

• Type QBASIC at DOS prompt
• Menu Choices
• File Edit View Search Run Debug Options
• Smart editor catches many Syntax errors
• REM is for remarks, such as your name and date

17
Programming Exercise
Create and run the following program CLS LET
grade1 3 LET grade2 2 LET grade3
3.25 LET gpa (grade1 grade2 grade3) /
3 PRINT grade1, grade2, grade3 PRINT
gpa END Change values for grades and run again.
18
Relational Operators

• equal to
• ltgt not equal to
• lt less than
• gt greater than
• lt less than or equal to
• gt greater than or equal to

19
Functions

• Prewritten routines that return a value based
  on one or more inputs
• Examples
• SQR(expression)
• INT(expression)
• Expression is a number, variable, or calculation

20
A Word to the Wise

• Complete as many of the odd number exercises as
  you can, checking your answers with those
  provided
• Get familiar with the mechanics of using the
  Qbasic editor

21
Strings

• Strings are anything other than numbers
• String constants are enclosed in double quotes
  ()
• String variable names end with a dollar sign ()

22
Example of Strings

• CLS
• LET me "Joe Komar "
• PRINT me
• PRINT "is one of the greatest instructors I
  have."
• LET me "Student name "
• PRINT me
• PRINT "is a great student."
• END

23
Strings

• Concatenation
• Use plus sign () between strings
• Get all ASCII characters with the character
  string function
• CHR(number)
• (see Appendix A for ASCII chart)

24
String Relationships

• identical to
• ltgt different from
• lt precedes alphabetically
• gt follows alphabetically
• lt precedes or identical
• gt follows or identical
• (special characters, digits, upper, lower)

25
String Related Functions

• LEFT(string, of characters)
• RIGHT(string, of characters)
• MID(string,beginning character,of characters)
• UCASE(string)
• LEN(string)
• INSTR(string,substring)
• VAL(string)
• STR(number)

26
String Functions Example

• CLS
• LET me "Joseph A. Komar "
• LET you "Komar "
• LET first LEFT(me, 6)
• LET last RIGHT(me, 6)
• LET middle MID(me, 8, 1)
• LET upper UCASE(me)
• LET length LEN(you)
• LET init INSTR(me, you)
• PRINT last, first, middle, upper
• PRINT length, init
• END

27
Data Input

• Data is stored in DATA statements
• DATA statements are read with the READ statement
  (RESTORE to go back to first DATA statement)
• Keyboard input is supplied by way of the INPUT
  statement

28
Sample DATA Statement

• CLS
• READ name, wage, hrs
• PRINT name wage hrs
• READ name, wage, hrs
• PRINT name wage hrs
• DATA "Joe Komar",10.33,40
• DATA "Susan Komar",15.40,45
• END

29
INPUT Statement

• CLS
• INPUT "Enter Name, wage rate, and hours" name,
  wage, hrs
• LET total wage hrs
• PRINT name " Hourly rate " wage "Total
  Wages" total
• END

30
Advanced PRINT

• PRINT zones -- four of 14 characters, one of 24
  characters
• TAB(n) -- positions cursor at position n across
  screen
• LOCATE r,c -- positions cursor at row r and
  column c
• PRINT USING -- uses picture or format for
  numbers

31
PRINT USING

• Format string
• ,.
• ,. -- fixed dollar sign
• ,. -- floating dollar sign
• \ \ -- reserves space for
  character strings
• See Appendix C for additional functionality

32
Example ofPRINT USING

• CLS
• PRINT " January February
  March "
• PRINT
• LET a "\ \ , ,
  , "
• PRINT USING a "House" 1010 1020 1030
• PRINT USING a "Beer" 210 220 130
• PRINT USING a "Other" 350 2300 220
• END

33
Output to PrinterLPRINT

• CLS
• LPRINT " January February
  March "
• LPRINT
• LET a "\ \ , ,
  , "
• LPRINT USING a "House" 1010 1020 1030
• LPRINT USING a "Beer" 210 220 130
• LPRINT USING a "Other" 350 2300 220
• END

34
Decision Structure
Then
Else
IF
Process 2
Process 1
35
Simple IF Statement

• CLS
• INPUT "Enter Revenues " revenue
• INPUT "Enter Costs " costs
• IF revenue gt costs THEN
• PRINT "Revenue is greater than costs"
• ELSE
• PRINT "Costs are greater than or equal to
  revenue"
• END IF
• PRINT "Profit " revenue - costs
• END

36
Nested IFs

• INPUT "Enter Revenue " revenue
• INPUT "Enter Costs " costs
• IF revenue costs THEN
• PRINT "Break even"
• ELSE
• IF costs lt revenue THEN
• PRINT "Profit " revenue - costs
• ELSE
• PRINT "Loss " costs - revenue
• END IF
• END IF
• END

37
IF with no ELSE

• CLS
• INPUT "Do you want instructions? (y or n) " ans
• IF ans "y" THEN
• PRINT "Here's more instruction"
• END IF
• PRINT "The next question is..."
• END

38
CASE logic (avoiding many nested IFs)

• SELECT CASE selector
• CASE valuelist1
• action1
• CASE valuelist2
• action2
• .
• CASE ELSE
• action if none of the above
• END SELECT

39
CASE logic example

• INPUT "Enter Grade (A,B,C,D, or F) " grade
• SELECT CASE grade
• CASE "A"
• points 4
• CASE "B"
• points 3
• CASE "C"
• points 2
• CASE "D"
• points 1
• CASE ELSE
• points 0
• END SELECT
• PRINT "Grade Points are " points
• END

40
Logical Connectors

• OR -- either item can be true
• (g lt 4) OR (m gt 7)
• (ans y) OR (ans Y)
• AND -- both items must be true
• (g lt 4) AND (m gt 7)
• NOT -- negative of the condition
• NOT (g lt 4)

41
Logical ConnectorsExample

• CLS
• INPUT "Do you want instructions? (y or n) " ans
• IF (ans "y") OR (ans "Y") THEN
• PRINT "Here are the instructions"
• END IF
• PRINT "Here's the next question"
• END

42
DO WHILE
NO
True?
YES
Process
43
DO WHILE Example

• CLS
• INPUT "Enter the beginning balance " balance
• INPUT "Enter the interest rate " interest
• LET years 0
• DO WHILE balance lt 1000000
• LET balance balance interest balance
• LET years years 1
• LOOP
• PRINT "In" years "years you will have
  1,000,000 dollars"
• END

44
DO UNTIL
Process
YES
True?
NO
45
DO UNTIL Example

• CLS
• LET ans Y
• DO UNTIL (ans "n") OR (ans "N")
• INPUT "Enter the beginning balance " balance
• INPUT "Enter the interest rate " interest
• LET years 0
• DO WHILE balance lt 1000000
• LET balance balance interest
  balance
• LET years years 1
• LOOP
• PRINT "In" years "years you will have
  1,000,000 dollars"
• INPUT "Do you want to run again? (y or n) "
  ans
• LOOP
• END

46
Looping Considerations

• Watch out for infinite loops (CtrlBreak)
• Nesting of loops is a very common practice
• Remember that the condition on the DO can be
  compound

47
FOR...NEXT Loops

• Used when you know exactly how many times a loop
  should be performed
• FOR i m TO n (STEP s)
• inumeric variable
• minitial value
• nterminal value
• sincrement (one if left off)
• End loop with NEXT i

48
FOR...NEXT Example

• CLS
• INPUT "Enter beginning population " pop
• INPUT "Enter beginning year " year
• INPUT "Enter rate of growth " rate
• INPUT "Enter the number of years " num
• FOR i year TO year num
• PRINT i,
• PRINT USING "," pop
• LET pop pop rate pop
• NEXT i
• END

49
Nesting of Loops

• Nested loops must be totally contained in the
  outside loop

50
Controlling Program FlowSummary

• IF..THEN...ELSE
• SELECT CASE
• AND, OR, NOT logical connectors
• DO WHILE...LOOP
• DO UNTIL...LOOP
• FOR...NEXT (STEP)

51
Arrays

• Same variable names with subscripts
• DIM (m TO n)
• mbeginning item number (usually 1)
• ntotal number of items in the array
• Often used with FOR...NEXT loops
• Essential in processing lists of like things --
  e.g. scores of students, names of presidents, etc.

52
Array Example

• CLS
• DIM name(1 TO 5)
• DIM score(1 TO 5)
• FOR i 1 TO 5
• INPUT "Enter name, score" name(i), score(i)
• NEXT i

53
Array Example (contd)

• LET high score(1)
• LET who name(1)
• LET which 1
• FOR i 2 TO 5
• IF score(i) gt high THEN
• high score(i)
• who name(i)
• which i
• END IF
• NEXT i
• PRINT "Student " which " scored " high "
  name " who
• END

54
Arrays, more generalized

• CLS
• INPUT "Enter the number of students" num
• DIM name(1 TO num)
• DIM score(1 TO num)
• FOR i 1 TO num
• INPUT "Enter name, score" name(i), score(i)
• NEXT i

55
Arrays, more generalized (contd)

• LET high score(1)
• LET who name(1)
• LET which 1
• FOR i 2 TO num
• IF score(i) gt high THEN
• high score(i)
• who name(i)
• which i
• END IF
• NEXT i
• PRINT "Student " which " scored " high "
  name " who
• END

56
Sorting

• Bubble Sort
• Uses the SWAP statement in BASIC
• SWAP var1,var2
• Requires (n-1) passes to completely order the
  array (where n is the number of items in the array

57
Sorting Example

• CLS
• INPUT "Enter the number of students" num
• DIM name(1 TO num)
• DIM score(1 TO num)
• FOR i 1 TO num
• INPUT "Enter name, score" name(i), score(i)
• NEXT i

58
Sorting Example (contd)

• FOR i 1 TO num - 1
• FOR j 1 TO num - i
• IF score(j) lt score(j 1) THEN
• SWAP name(j), name(j 1)
• SWAP score(j), score(j 1)
• END IF
• NEXT j
• NEXT i

59
Sorting Example (contd)

• PRINT "Highest to lowest score"
• PRINT
• FOR i 1 TO num
• PRINT score(i), name(i)
• NEXT i

60
Sorting -- First output

• Highest to lowest score
• 95 James
• 88 Winsock
• 73 Komar
• 68 Anderson
• 56 Tornado

61
Sorting Example (contd)

• FOR i 1 TO num - 1
• FOR j 1 TO num - i
• IF name(j) gt name(j 1) THEN
• SWAP name(j), name(j 1)
• SWAP score(j), score(j 1)
• END IF
• NEXT j
• NEXT i

62
Sorting Example (contd)

• PRINT
• PRINT "Alphabetical List"
• PRINT
• FOR i 1 TO num
• PRINT score(i), name(i)
• NEXT i
• END

63
Sorting -- Second output

• Alphabetical List
• 68 Anderson
• 95 James
• 73 Komar
• 56 Tornado
• 88 Winsock

64
Searching

• Sequential -- used with an unordered array -- see
  example of finding the highest score
• Binary -- used with a sorted array
• Start in the middle
• Determine which way to go from there
• Can be used in day-to-day searching

65
Searching Example

• INPUT "Enter the student to find" find
• LET first 1
• LET last num
• LET found 0

66
Searching Example (contd)

• DO WHILE (first lt last) AND (found 0)
• LET middle INT((first last) / 2)
• SELECT CASE name(middle)
• CASE find
• LET found 1
• CASE IS gt find
• LET last middle - 1
• CASE IS lt find
• LET first middle 1
• END SELECT
• LOOP

67
Searching Example (contd)

• IF found 1 THEN
• PRINT "Found " find
• ELSE
• PRINT find " not found"
• END IF
• END

68
Arrays Summary

• Variable name with a subscript
• name(number)
• DIM (m TO n)
• Bubble sort -- arranges item in array
• Searching
• Sequential with an unordered list
• Binary with an ordered list

69
Subprograms

• Performs one or more related tasks
• Written as a separate part of the program
• Accessed via a CALL statement
• SUB subprogramname
• statements
• END SUB
• May pass parameters (arguments)

70
Subprogram Example

• CLS
• INPUT "Enter two numbers" first, second
• CALL addem(first, second)
• END
• SUB addem (a, b)
• LET c a b
• PRINT a " " b " " c
• END SUB

71
Subprogram Purpose

• Allows for modularity of large programs
• Allows for reusable program code
• Frequently executed code can be isolated
• Code can be changed in one place only
• Subprograms can call other subprograms

72
Subprogram to Main Program

• CLS
• INPUT "Enter two numbers" first, second
• CALL addem(first, second, sum)
• PRINT "The sum is " sum
• END
• SUB addem (a, b, c)
• LET c a b
• PRINT a " " b " " c
• END SUB

73
Subprogram Results

• Enter two numbers? 12,13
• 12 13 25
• The sum is 25

74
Subprogram Argument Passing

• Order of arguments is critical
• Arguments must match in kind -- numeric with
  numeric, string with string
• Arguments passed can be expressions
• CALL (x5,y15,z)
• Can pass arrays -- e.g., name()
• Variables are local to subprograms

75
Main Program and SUBs

• Main program can have three components
• Input Process Output
• SUBs then perform each of these functions
• SUBs can, themselves be main programs

76
Sequential File Creation

• Open the file for writing
• OPEN filespec FOR OUTPUT AS n
• Use the WRITE statement to write data into the
  file
• WRITE n, variablelist
• Close the file when done
• CLOSE n

77
File Creation Example

• CLS
• OPEN "Ajunk.dat" FOR OUTPUT AS 1
• WRITE 1, "Komar", 25000
• WRITE 1, "Anderson", 32000
• WRITE 1, "Johnson", 43000
• CLOSE 1
• END

78
File Creation Example

• "Komar",25000
• "Anderson",32000
• "Johnson",43000

79
Appending to a File

• Open the file for appending
• OPEN filespec FOR APPEND AS n
• Write to the file
• WRITE n, variablelist
• Close the file when done
• CLOSE n

80
Reading a File

• Open the file for reading
• OPEN filespec FOR INPUT AS n
• Read data from the file
• INPUT n, variablelist
• Use the EOF(n) function to detect end-of-file
• Close the file when done
• CLOSE n

81
Reading Example

• CLS
• OPEN "Ajunk.dat" FOR INPUT AS 1
• DO WHILE NOT EOF(1)
• INPUT 1, name, salary
• PRINT name, " makes ", salary
• LOOP
• END

82
Reading example

• Komar makes 25000
• Anderson makes 32000
• Johnson makes 43000