CSE 113

1
CSE 113

• Week 5
• February 11 - 15, 2008

2
Announcements

• Module 2 due 2/15
• Exam 3 is on 2/15
• Module 3 due 2/22
• Exam 4 is on 2/25
• Module 4 due 2/29

3
Highlights

• What if we wanted to change all of the pixels in
  a picture to black?
• We need to access all of the pixels of the
  picture one at a time and then change their color
  to black.

4
Highlights

• We cant do this simply by inputting each
  coordinate of the pixels and changing them,
  because it only works for certain images, not all
  images.
• What we want to do is repeat the process of
  getting a pixel and changing its color.

5
Highlights

• We need a way to help us repeat.
• Repetition is a key element of computation.
• One way to have a program repeat is to add a loop
  to our program.
• The loop we will look at first is a for-loop

6
Highlights

• The for-loop is a counting loop, so much of the
  syntax needed helps us to set up the counting of
  how many times the loop should repeat.
• For-loop syntax
• for(initialization test increment)
• //loop body

7
Highlights

• initialization
• Create a variable that is our loop counter and
  give it a starting value
• test
• Test to tell us when to stop the counting
• increment
• Increments the counter after each time the loop
  body is executed

8
Highlights

• We can start a count with the first pixel in a
  row/column and continue counting until the end of
  the row or column
• Remember that we can tell the width and height of
  a picture by calling the appropriate methods on it

9
Highlights

• In order to go through all the pixels (width x
  height), we will need a system of two loops, one
  that loops through the columns, and the other
  that loops through the rows.
• Putting them together allows us to go through all
  the rows and columns in the picture.