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Recitation 1 — Numbers, Strings, Images

Skills: 1​

Reading: 3.1​

1. T-Shirt Shop Math​

Goal: Practice arithmetic expressions and order of operations.

  1. Calculating Cost

    • You sell custom T-shirt designs for $12 each. However, every design requires a $3 setup fee.
    • Write an expression to calculate the total cost for 5 identical T-shirts for a custom design.
    • Then, write a second expression for 7 identical T-shirts for a design.
    • Compare the results. Hint: Use parentheses where needed: (2 * 4) + 4, etc.

  2. Rectangular Poster

    • You also print posters. A client wants a 24" by 36" poster. The price is based on the perimeter of the poster times $0.10.
    • First, compute the perimeter with an expression (remember Perimeter = 2 * (width + height)).
    • Then, multiply that perimeter by 0.10 to find the cost.
    • What happens if you forget parentheses around (width + height)?

2. String Surprises​

Goal: Experiment with strings.

  1. Saving a Tagline

    • Your T-shirt shop’s tagline is: “Designs for everyone!”
    • Type it into Pyret as a string.
    • Now omit one of the quotes and see the error.
    • Fix the error so your string prints correctly.

  2. Color Inventory

    • You keep track of colors as strings. For instance: "red", "blue", "gold".
    • What happens if you try to + them (e.g. "red" + "blue")?
    • Reflect: + works on both numbers and strings. What happens if you do 1 + "blue"?

3. Make a Traffic Light​

Goal: Practice layering shapes.

  1. Frame

    • Start with a solid black rectangle that is tall and narrow (e.g., rectangle(40, 100, "solid", "black")). This will be the traffic light’s body.

  2. Lights

    • Overlay three colored circles (red, yellow, green) on top of that rectangle, spaced in a vertical stack.
    • You may do this by carefully using above with each circle and overlaying them onto the rectangle.
    • Alternatively, overlay them one by one in the correct positions using functions like overlay-xy.

  3. Challenge

    • Can you add a small rectangular “pole” at the bottom?
    • How might you use above or beside to position the pole?

4. Broken Code Hunt​

Goal: Identify type mismatches or wrong arguments.

Each of these snippets has an error. Try them in Pyret, read the error message, and fix it.

   # Goal: A rectangle with width 50 and height 20, solid black
   rectangle(50, "solid", 20, "black")
  • Hint: Check the order and types of arguments that rectangle expects.
circle(30, solid, "red")
  • Hint: The second argument must be a string ("solid" or "outline").

5. Create a Flag or Shield​

Goal: Experiment more with images.

  1. Flag Design

    • Invent a simple flag using at least three shapes.
    • For instance, many flags have stripes (rectangles) above or beside each other, or shapes overlaid in the center.
    • Example steps:
      • Make one large rectangle as the background.
      • Overlay a smaller shape (circle, star, or rectangle) in the upper left.
      • Possibly add a vertical stripe on the right side.

  2. Shield Variation

    • Alternatively, make a shield shape (maybe a rotated square to get a diamond) overlaid with a circle or star.
    • Try out rotate(45, square(100, "solid", "gray")) to get a diamond shape.
    • Layer shapes on top of it for an emblem.

  3. Share

    • Show your neighbor.
    • If time allows, label your shapes with text (e.g., overlay(text("Go!", 20, "black"), your-shield)).