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Lesson 3 homework

Three triangles. Every one of them is the star triangle from the lesson with different numbers — the pseudocode barely changes; only the math does.

Work like a programmer on each one:

  1. Write the pseudocode in English first
  2. Make a have/want table: what does the loop give you, what does the row need?
  3. Find the math that turns have into want

  4. Translate to Python

  5. Make as many mistakes as you like

  6. Don't give up

Problem 1 — upside down

Flip the lesson's triangle: the widest row comes first.

Output

**********
*********
********
*******
******
*****
****
***
**
*

Code

  • Start from the star triangle program — the pseudocode is the same, one number changes
  • Have/want table: row_num goes 1, 2, 3, ... — but row 1 needs 10 stars, row 2 needs 9, row 3 needs 8...
  • What math turns 1 into 10, 2 into 9, and 3 into 8?

Problem 2 — slope on the left

Same triangle as the lesson, but leaning the other way: the slope runs from top-left down to bottom-right, and the straight edge is on the right.

Output

         *
        **
       ***
      ****
     *****
    ******
   *******
  ********
 *********
**********

Code

  • Look carefully at row 1: the star is pushed to the right by spaces. A space is a real character, and you can print it: print(" ", end="")
  • Each row now has two parts: first the spaces, then the stars. Two parts means two inner loops, one after the other, inside the outer loop
  • Write the pseudocode for the two parts first, then make two have/want tables — one for spaces, one for stars
  • Count from the output: row 1 has 9 spaces + 1 star, row 2 has 8 spaces + 2 stars... row 10 has 0 spaces + 10 stars

Problem 3 — upside down, slope on the left

Now flip problem 2: widest row first, straight edge still on the right.

Output

**********
 *********
  ********
   *******
    ******
     *****
      ****
       ***
        **
         *

Code

  • Same two-part rows as problem 2 — only the math changes
  • Count the spaces and stars in the first few rows and build the have/want tables
  • If your problem 1 and problem 2 tables were right, this one is just combining them

When all three run, look at your four programs side by side — the lesson's triangle and these three. Same pseudocode, same skeleton, four different pictures. That is what the have/want math controls.