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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

Pacing Guide

Duration Description
5 minutes Welcome, attendance, bell work, announcements
15 minutes Lecture and examples
25 minutes Activity - Squares and Triangles
10 minutes Debrief and wrap-up

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

BJC Lecture Suggestions

####Background Information for Instructors

  • BJC Video Suggestion: BJC Lecture 4: Functions
  • SIRI-EVI 0:00-1:00
  • Functions & Generaliztions (Function Basics) 1:00-3:45
  • More Terminology (from Math) Boolean etc 3:47-6:10
  • Types of Input (Sentences, words, characters, digits) 6:12-8:00
  • Functions (Explanations of Use-can be tied in to loops, and inputs) 8:00-9:55
  • MIT Scratch --> BYOB SNAP ( Development of SNAP, DEMO) 10:00-11:30
  • Functions-1 (BYOB-Custom Blocks) & Generalization 11:30-14:50
  • Functions-2 (Join Block) Domain and Range 14:52-17:50
  • Types of Blocks 18:15-19:45
  • Recursion Preview 19:50-27:40
  • Functional Programming Summary 27:40- End
  • Big concepts narrow down to functions

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