Introduction to Lists and Iteration

Discussion Question: How would you build a slide-show of images/text?

Instructor Demo: if-else solution to this problem

• Add a button and upload three images
• set Button.BackgroundImage to first image in designer
• In blocks editor, use if-else-else to sequence through images on each button click. Go back to first image after last.
• Note how file name of loaded image is used and must be set exactly.

Discuss if-else solution

• Would it be easy to add another item?
• Could the images shown be user generated?

List Solution

Store images in a list variable. Use an index variable to walk through the list

• List-- a single variable (name) representing multiple memory cells
• Index -- a number representing the current position in the list. 1 is the first position.
• Important List functions: select list item, add items to list

Instructor demo: sketch or code blocks for letting user walk through list

• start index at 1
• on screen.initialize:
• on nextButton.Click
• reaching the end of list

Discussion: Compare If-Else and List solution

• What if number of items changes, which is easier to change?
• What if user enters images, will if-else solution work?