Free PCEP Using the `else` block in loops Questions and Answers 1 — Questions and Answers
Question 1: What is the output of the following code?
```python
for i in range(3):
print(i)
else:
print('Done!')
```
- 0
1
2
- 0
1
2
Done! (Correct answer)
- Done!
- A syntax error occurs.
Correct answer: 0
1
2
Done!
The `else` block in a `for` loop executes only if the loop completes its entire iteration without being terminated by a `break` statement. In this case, the loop finishes normally, so 'Done!' is printed after the numbers 0, 1, and 2.
Question 2: What is the output of the following code?
```python
for num in [1, 2, 3, 4]:
if num == 3:
break
print(num)
else:
print('Finished.')
```
- 1
2 (Correct answer)
- 1
2
Finished.
- 1
2
3
- 1
2
3
Finished.
Correct answer: 1
2
The `break` statement terminates the loop when `num` is 3. Because the loop did not complete its full iteration, the `else` block is skipped entirely. Only the numbers before the `break` are printed.
Question 3: What is the output of this `while` loop?
```python
i = 5
while i > 0:
i -= 1
if i == 2:
continue
print(i)
else:
print('Loop over.')
```
- 4
3
1
0
- 4
3
1
- 4
3
1
0
Loop over. (Correct answer)
- 4
3
2
1
0
Loop over.
Correct answer: 4
3
1
0
Loop over.
The `continue` statement skips the current iteration but does not terminate the loop. The loop continues until `i` becomes 0, at which point the condition `i > 0` is false. Since the loop completed normally, the `else` block is executed.
Question 4: Under which circumstance is the `else` block of a loop NOT executed?
- When the loop condition becomes false.
- When a `break` statement is executed. (Correct answer)
- When a `continue` statement is executed.
- When the loop iterates over an empty sequence.
Correct answer: When a `break` statement is executed.
The primary purpose of the `else` block in a loop is to run code when the loop finishes its iterations naturally. If the loop is exited prematurely using a `break` statement, the `else` block is skipped.
Question 5: What will be printed to the console?
```python
for char in 'PCEP':
print(char)
break
else:
print('End of string')
```
- P
C
E
P
End of string
- P
End of string
- P (Correct answer)
- End of string
Correct answer: P
The loop starts with the first character 'P' and prints it. Immediately after, the `break` statement is encountered, which terminates the loop. Since the loop was terminated by `break`, the `else` block is not executed.
Question 6: Consider the following code. What is the output?
```python
items = []
for item in items:
print(item)
else:
print('No items found.')
```
- An error occurs.
- The program produces no output.
- No items found. (Correct answer)
- []
Correct answer: No items found.
When a `for` loop is given an empty sequence (like an empty list), it does not execute its body at all. It is considered to have completed 'normally' without any iterations. Therefore, the `else` block is executed.
Question 7: What is the output of this code snippet?
```python
n = 3
while n > 0:
n -= 1
print(n)
else:
if n == 0:
print('Loop ended.')
```
- 2
1
0
Loop ended. (Correct answer)
- 3
2
1
- 2
1
0
- 3
2
1
Loop ended.
Correct answer: 2
1
0
Loop ended.
The `while` loop runs until `n` becomes 0. The loop prints 2, 1, and 0. When `n` is 0, the condition `n > 0` becomes false, and the loop terminates. Since it terminated normally, the `else` block is executed. Inside the `else` block, the condition `n == 0` is true, so 'Loop ended.' is printed.
