Arrays

1
Arrays
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An array is a collection

• The Dinner offers an array of choices.
• In computer programming, an array is a collection
  of variables of the same data type
• Arrays can be collections of ints, chars, floats,
  booleans,, any data type.
• Example String---a collection of characters

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What good is a collection?

• Can you think of times when it would be useful to
  store a collection of values?
• How about the display on the monitor---isnt that
  a collection of pixel values?
• Test grades---isnt that a collection
• College courses
• The path of a missile
• The names of all students
• Just about any list
• We use collections all of the time!

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How to Create an array

• An array of integers
• int numbers 1,2,3,4,5,6,7,8,9,10
• This is an array with 10 elements
• An array with no values specified
• int numbers new int10
• This is an array large enough to store 10
  elements but the elements have not been specified

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Creating arrays

• An array of 10 doubles
• double tomsGrades 0,1.1,2.2,3,4.4,5.5,6,7,8
  ,9.9
• double fredsGrades new double10
• An array of 10 characters
• char sally a,b,c,b,,a
• String sue abcbacdfaaaa ?this is actually
• more than just an array
• char jane new char26

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Accessing the elements

• Each element in an array has a name---its the
  array plus an offset also called an index
• int evens 2, 4, 6, 8, 10

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for-loops and arrays

• They were designed to be used together
• int numbers new int100
• for (int i 0 ilt100 i)
• numbersi i
• OR
• int numbers new int100
• for (int i 0 iltnumbers.length i)
• numbersi i

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Let it Snow

• int num 11
• int spacing 40
• int diameter 20
• float x new floatnum
• float y new floatnum
• void setup()
• size(400, 400)
• noStroke()
• smooth()
• fill(255, 180)
• for (int i 0 i lt num i)
• xiispacing
• yirandom(0,spacing)
• 
  //continued on next page

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Snow (continued)

• void draw()
• background(0)
• for (int i 0 i lt num i)
• ellipse(xi, yi, diameter, diameter)
• // move down the canvas
• for (int i 0 i lt num i)
• (yi)

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Another example

• int numLines 12
• float x new floatnumLines
• float speed new floatnumLines
• float offset 8 //
  Set space between lines
• void setup()
• size(100, 100)
• smooth()
• strokeWeight(10)
• for (int i 0 i lt numLines i)
• xi i
  // Set initial position
• speedi 0.1 (i / offset)
  // Set initial speed
• 
  //continued on next page

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Continued

• void draw()
• background(204)
• for (int i 0 i lt x.length i)
• xi speedi // Update
  line position
• if (xi gt (width offset)) // If off
  the right,
• xi -offset 2 // return
  to the left
• float y i offset // Set
  y-coordinate for line
• line(xi, y, xi offset, y offset)
  // Draw line

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Your Turn

• Modify the Snow example presented earlier to make
  the snow flakes reappear at the top of the canvas
  once they have moved off the bottom of the canvas.

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Review and More Fun With Arrays

• int num 50
• int x new intnum
• int y new intnum
• void setup()
• size(100, 100)
• noStroke()
• smooth()
• fill(255, 102)
• //continued on next page

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More Fun With Arrays (cont)

• void draw()
• background(0)
• // Shift the values to the right
• for (int i num - 1 i gt 0 i--)
• xi xi-1
• yi yi-1
• // Add the new values to the beginning of the
  array
• x0 mouseX
• y0 mouseY
• // Draw the circles
• for (int i 0 i lt num i)
• ellipse(xi, yi, i / 2.0, i / 2.0)