Lesson 2.1: Loops

Learning Objectives

Students will be able to...

• Define "loop" in a programming context
• Explain why loops are useful
• Implement simple repeat and forever loops in SNAP
• Utilize loops to reduce redundancy in code

Materials/Preparation

• Lab 2.1 handout - Squares and Triangles Redux (Download in MS Word) (Link to PDF)

Pacing Guide

Instructor's Notes

1. Lecture

   1. Introduce and discuss concepts of code redundancy and readability
      • Remind students that a program can be written in many different ways that are functionally equivalent.
      • Ask students to speculate as to why one version of a program might be better or worse.
        • Possible answers: more efficient (in time or space), shorter code, more elegant/readable code
      • Use this example to demonstrate unreadable code
        • Show students the code, ask what it does, then ask if they can think of ways to improve it
        • Attempt to get students to realize that the code is redundant and could be simplified if there were a way to execute a block of code more than once
   2. Introduce loops
      • Begin with general definition: A type of block that causes other code to run multiple times in succession
      • Introduce SNAP specific loops:
        • runs the body of the loop the specified number of times
          • Number of iterations can be a value, variable, or reporter
        • runs the body of the loop nonstop until the script is ended
          • Can be stopped either by clicking the stop sign or by any version of
        • runs the body of the loop until the specified condition becomes true
          • Save detailed discussion of this loop until conditionals are introduced

   3. Walk through examples of and

      • Emphasize usefulness in reducing redundancy and complexity, especially for repetitive tasks
      • Simple examples are here
2. Activity
   • Direct students to complete "Squares and Triangles Redux" individually.
     • If available, students should use their solutions to Lab 1.3 ("Squares and Triangles and Stars, Oh My!") as a starting point. Ensure students "Save as..." before starting on the new lab to not overwrite their original project (part 1.1).
       • If student solutions for Lab 1.3 are not available, or are not correct, provide a correct implementation (download the .xml file and import it into SNAP).
     • Encourage students to try to use as few blocks and have as little code duplication as possible to draw each shape while still creating understandable scripts.
     • Once students complete part 2.1, the remaining parts should go much more quickly as they all follow the same basic pattern.
3. Debrief
   • Discuss one or two student solutions to part 2.2
     • Ask students to think about what the code would look like without loops
   • Discuss one or two students solutions to part 3.1
     • Point out how unwieldy the code for these two shapes would be without loops

Accommodation/Differentiation

• More advanced students can add additional shapes, including a five-pointed star without interior lines.

  *  Particularly advanced students can be encouraged to build pictures by combining multiple shapes (e.g. a house built of squares of various sizes).
  

  Lab 2.1 Solution