What will be displayed after the following code is executed assuming num was initially set to zero?

for n in range(0, 20, 5):
num += n
print(num)

Question

What will be displayed after the following code is executed assuming num was initially set to zero?

for n in range(0, 20, 5):
  num += n
print(num)

BlackTom AI · Accepted Answer

range(0, 20, 5) generates the sequence 0, 5, 10, 15 (start included, stop excluded, step of 5), so num will accumulate those values via num += n.

1. Relevant knowledge points and concepts
- Python range(start, stop, step) includes start, increments by step, and stops before stop (stop is exclusive).
- The += operator increments a variable by the right-hand value (num += n is equivalent to num = num + n).
- The print function outputs the final value of num after the loop.

2. Complete step-by-step reasoning
- Initial condition: num = 0.
- The loop: for n in range(0, 20, 5): iterates n over 0, 5, 10, 15 in that order.
- Each iteration updates num by adding the current n.

3. Intermediate calculation steps
- First iteration: n = 0 -> num = 0 + 0 = 0
- Second iteration: n = 5 -> num = 0 + 5 = 5
- Third iteration: n = 10 -> num = 5 + 10 = 15
- Fourth iteration: n = 15 -> num = 15 + 15 = 30

4. Why the correct answer is correct
Because the loop adds each value produced by range(0, 20, 5) to num, the final accumulated sum after all iterations is 30. The stop value 20 is not included in the range, so 20 is not added.

5. Why other options are incorrect
- "25": would require the series to be 0+5+10+10 or 5+20 etc.; it does not match actual range values.
- "5
10
15": represents printing each n on separate lines, but the code prints num once after the loop, not the loop variable in each iteration.
- "20": would result if only 5+15 (or some different combination) were added; it ignores either 0 or one of the values. The actual sum includes 0,5,10,15 = 30.

6. Conclusion
Final printed output is 30, which matches the provided correct answer.

What will be displayed after the following code is executed assuming num was initially set to zero? for n in range(0, 20, 5): num += n print(num)单项选择题

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