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Class 8 Computer Science — Blocks and indentation

Read a program's indentation to say which lines belong to which block, and how often each line runs.

Name: ________________________

1.Sort each line of this program by how many times it runs.
```
total = 0
for n in range(1, 4):
    total = total + n
    print(n)
print(total)
print(total * 2)
```
Groups: Runs once · Runs three times
- total = 0
- print(n)
- print(total * 2)
- total = total + n
- print(total)
2.This program prints four numbers. Put them in the order they appear on the screen.
```
total = 0
for n in range(1, 4):
    total = total + 5
    print(total)
print(total - 12)
```
- 10
- 15
- 3
- 5

3.This one has an else branch as well. What is total at the end?

total = 0
for n in range(1, 5):
    if n > 2:
        total = total + 1
    else:
        total = total + 100

4.This program was meant to show the total once, at the very end, but it shows a number four times over. What went wrong?
```
total = 0
for n in range(1, 5):
    total = total + n
    print(total)
```
- a) The printing line is indented, so it sits inside the loop and runs every trip round
- b) The loop has been written to go round one time too many
- c) The total is set to 0 on the wrong line of the program
- d) A program is only allowed to print one number in total
5.Both of the printing lines are indented here. How many numbers does it print?
```
for n in range(1, 4):
    print(n)
    print(99)
```
6.The last line has been brought back out to the left. What is total at the end?
```
total = 0
for n in range(1, 4):
    total = total + 10
total = total + 1
```

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

total = 0
for n in range(2, 6):
    total = total + n
print(total)
print(total * 2)

8.One of these four lines runs a different number of times from the other three. Which one?
```
for n in range(1, 4):
    print(n)
    print(n * 2)
    print(n * 3)
print(0)
```
- a) The line printing n times 2
- b) The line printing n
- c) The line printing n times 3
- d) The line printing 0

Answer key — Class 8 Computer Science — Blocks and indentation

1. total = 0 → Runs once; total = total + n → Runs three times; print(n) → Runs three times; print(total) → Runs once; print(total * 2) → Runs once
2. 1. 5 2. 10 3. 15 4. 3
3. 202
4. a) The printing line is indented, so it sits inside the loop and runs every trip round
5. 6
6. 31
7. 28
8. d) The line printing 0