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Grade 8 Computer Science — Loops inside loops

Work out how many times the body of a loop inside another loop runs, and in what order the two counters change.

Name: ________________________

  1. 1.Follow this code by hand. What is count at the end? Notice that the inner range depends on the outer counter.

    count = 0
for row in range(1, 5):
    for star in range(1, row + 1):
        count = count + 1

  2. 2.Follow this code by hand. How many numbers does it print?

    for a in range(1, 3):
    for b in range(1, 3):
        print(b)

  3. 3.In this program, which line runs the greatest number of times?

    for a in range(1, 6):
    print(a)
    for b in range(1, 4):
        print(b)
print(0)
    • a) The line printing a
    • b) The line printing b
    • c) The line printing 0
    • d) The heading of the inner loop

  4. 4.In each of these, one loop sits inside another with a single line at the deepest level. Match each pair of ranges to how many times that line runs.

    • range(1, 3) outside, range(1, 6) inside
    • range(1, 4) outside, range(1, 8) inside
    • range(1, 5) outside, range(1, 3) inside
    • range(2, 5) outside, range(1, 5) inside
    • range(1, 10) outside, range(1, 3) inside
    • 10
    • 12
    • 21
    • 18
    • 8

  5. 5.In each of these, one loop sits inside another with a single line at the deepest level. Sort each one by how many times that line runs.

    Groups: Eight times · Fifteen times

    • range(1, 3) outside, range(1, 5) inside
    • range(4, 8) outside, range(1, 3) inside
    • range(1, 6) outside, range(2, 5) inside
    • range(3, 8) outside, range(4, 7) inside
    • range(2, 6) outside, range(3, 5) inside
    • range(0, 5) outside, range(0, 3) inside

  6. 6.Follow this code by hand. What is the second number it prints?

    for a in range(1, 4):
    for b in range(1, 4):
        print(a * 10 + b)

  7. 7.Follow this code by hand. What is count at the end?

    count = 0
for a in range(1, 5):
    for b in range(1, 6):
        count = count + 1

  8. 8.Follow this code by hand. How many times does the most deeply indented line run?

    for a in range(1, 4):
    for b in range(1, 5):
        print(a * b)

Answer key — Grade 8 Computer Science — Loops inside loops

  1. 1. 10
  2. 2. 4
  3. 3. b) The line printing b
  4. 4. range(1, 3) outside, range(1, 6) inside → 10; range(1, 4) outside, range(1, 8) inside → 21; range(1, 5) outside, range(1, 3) inside → 8; range(2, 5) outside, range(1, 5) inside → 12; range(1, 10) outside, range(1, 3) inside → 18
  5. 5. range(2, 6) outside, range(3, 5) inside → Eight times; range(1, 6) outside, range(2, 5) inside → Fifteen times; range(1, 3) outside, range(1, 5) inside → Eight times; range(0, 5) outside, range(0, 3) inside → Fifteen times; range(4, 8) outside, range(1, 3) inside → Eight times; range(3, 8) outside, range(4, 7) inside → Fifteen times
  6. 6. 12
  7. 7. 20
  8. 8. 12