Programming With Arrays

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Arrays are Awesome!
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Questions

• What is a variable?

• A storage location in RAM
• A name of a storage location
• An identifier for our data
• . . .

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Questions

• How does the data get input?

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Ways to enter data into RAM
If we want to store 5 in X
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We can assign X to represent 5.
LET X 5 or X 5
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Ways to enter data into RAM
If we want to store 5 in X And we have this line
in our program DATA 5
5
READ X
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Ways to enter data into RAM
If we want to store 5 in X
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INPUT Type a 5 , X
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Questions
How many values can be stored in one location at
one time?
X
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How many values can be stored in X at once?
x
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Just one number at a time
x
5
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So whats the problem?
Lots of stuff for this address!
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Heres the problem
It doesnt work!
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• PROBLEM STATEMENT
• A program is needed that will read in the number
  of hours different people watched TV last week.
  The program should calculate the average viewing
  time and display a report showing each person,
  each persons hours, and the difference from the
  average viewing time.

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• Name Hours Difference
• P. Busch 1 -3
• J. Drake 5 1
• T. Zekly 11 7
• M. Blas 0 -4
• C. Carstens 4 0
• D. Zongas 3 -1
• Average 4 hours of TV viewing

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• Name Hours
• P. Busch 1
• J. Drake 5
• T. Zekly 11
• M. Blas 0
• C. Carstens 4
• D. Zongas 3
• Average 4 hours of TV viewing

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Problems

• We cant know the average until we exit the loop!
• The TotalHours and Count variables
• arent finished accumulating until then.

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Problems

• We cant know the difference from the
  averageEVER!
• The Hours for each viewer are lost by the time
  the loop ends ( we can finally calculate the
  average).

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Problems

• Only one value can be stored by a variable at one
  time!
• Each READ statement gets new values for the
  variables old ones are destroyed.

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Solutions?

• Have separate variables for each persons
  hoursdont use a loop.
• Double up on the DATA lines. READ through once
  to calculate the average. READ through again to
  PRINT the report.
• ?

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How depressing
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An easier way!!
Arrays are Awesome!
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Arrays are

• Data structures that store multiple items!
• Just like lists!
• Searchable!
• Sortable!

? ? Is that a word?

• Variables with subscripts!
• Awesome!

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Variables vs. Arrays
Groceries
Milk
Bread
Eggs
Butter
Jelly
EOF
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Variables vs. Arrays
Groceries
Groceries( )
Food
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Arrays can store multiple items!
Hours( )
Name( )
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Arrays are lists
A number goes here
Groceries( )
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DEFINITIONS

• Array A set of related data items, with the same
  variable name, that can be stored in RAM at the
  same time
• Element One of the individual items in an array
• Subscript A number (in parentheses) designating
  an array element

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Use DIM to Create an Array

• The computer needs to know the address (array
  variable name) and information about the elements
  (1st and last numbers).
• DIMension arrays at the beginning of the program.
• DIM Groceries(1 TO 5)
• DIM Name(1 TO 6),Hours(1 TO 6)

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Use any input to Fill an Array

• LET Groceries(1)Milk
• LET Groceries(2)Eggs

etc.
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READ is a common way

• To fill an array you would use a loop to fill
  the different elements with different values.

FOR X 1 TO N N is how many READ
Name(X) NEXT X DATA Al DATA Bob
DATA Al, Bob works to fill a single array!
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Or Input with INPUT

• FOR X 1 TO N
• INPUT Type a ,Num(X)
• NEXT X

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Parallel arrays are easy!

• N 6
• DIM City(1 TO N), Team(1 TO N)
• FOR X 1 TO N
• INPUT City , City(X)
• INPUT Team name ,Team(X)
• NEXT X

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W O W ! ! !
Team( )
City( )
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PRINTing data in an array

• Just put the PRINT statement inside a loop and
  remember to

use the subscript!
FOR X 1 TO N PRINT Name(X) NEXT X
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Array Program Algorithm
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Create the Array
Groceries( )
DIM Groceries(1 TO 5)
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Create the Array
Better way N 5 DIM Groceries(1 TO N)
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Fill the Array
Groceries(1) Milk INPUT Groceries(1) READ
Groceries(1)
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Fill the Array
with READ or INPUT in a loop!
FOR X 1 TO N READ Groceries(X) NEXT X
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Print the Array
with PRINT in a separate loop!
FOR X 1 TO N PRINT Groceries(X) NEXT X
FOR X N TO 1 STEP -1 PRINT
Groceries(X) NEXT X
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Sample Program (SPORT1.BAS)
This program stores 5 sports CLS Create array N
5 DIM Sport(1 TO N)
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Sample Program (SPORT1.BAS)
Fill array FOR X 1 TO N INPUT Type a sport
,Sport(X) NEXT X
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Sample Program (SPORT1.BAS)
Print array FOR X 1 TO N PRINT
Sport(X) NEXT X END
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Now were ready for some
Awesome Array
P R O G R A M S !