CSE 113 Week 5 February , 2008

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

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.

Highlights  We can’t 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.

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

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 }

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

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

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.