Python中while循环与if语句替换>=为>为何效果不同？

Let's break this down step by step to understand what's happening with each change!

First, let's recap your original code for reference:

entry = 0
sum = 0
print("Enter numbers to sum, negative number ends list: ")
while entry >= 0:
    entry = int(input())
    if entry >= 0:
        sum += entry
print("Sum =", sum)

1. Why swapping >= with > in the if statement doesn't change anything? #

The if statement here checks if the input number is non-negative before adding it to sum. When you replace >= with >, you're now only adding positive numbers instead of non-negative ones (so 0 gets excluded from the sum).

But here's the catch: adding 0 to sum doesn't actually change the total. Whether you include 0 or not, the final sum will be identical. For example:

• If you input 0 then -1, the original code adds 0 to sum (sum stays 0), while the modified code skips adding 0 (sum also stays 0).
• If you input 5, 3, -1, both versions add 5+3=8 to sum.

Since 0 doesn't affect the sum, the program's output looks exactly the same even with this change.

2. Why swapping >= with > in the while loop makes the program exit immediately? #

Look at the initial value of entry: you set it to 0 at the start.

• In the original code, the while entry >=0 condition is true (0 >=0 is true), so the loop runs and prompts you for input.
• When you change the condition to while entry >0, the initial check fails (0 >0 is false). The loop never runs at all—so the program skips straight to printing Sum = 0 without letting you enter any numbers.

That's why this change breaks the entire input flow!

内容的提问来源于stack exchange，提问作者JayOsso