为什么这是以下代码的输出？

Question

I am having trouble understanding why the output for this code is 16. I apologize if I am formatting anything incorrectly, I am new to coding.

I have written the code a couple times to make sure I was formatting it correctly

x = 1
while x < 10:
    x += x
print(x)

The output that is printing for me is 16.

Answer 1

It makes sense to me. The statement x += x is equivalent to x *= 2 , doubling x .

To help you understand, try printing x after every iteration:

x = 1
while x < 10:
    x += x
    print(x)

Output:

2
4
8
16

On each step:

2    # greater than 10? no
4    # greater than 10? no
8    # greater than 10? no
16   # greater than 10? yes, stop loop

Answer 2

Maybe changing the location of the print(x) could help you:

x = 1
print(1)
while x < 10:
    x += x
    print(x)

Output:

1
2
4
8
16

As you can see there is a common patron. Each iteration of the while duplicates the before value of x (that is due to x += x , which could be interpreted as double the x).

Then, the condition while x < 10 is quite simple.

1     # Less than 10. Keep looping.
2     # Less than 10. Keep looping.
4     # Less than 10. Keep looping.
8     # Less than 10. Keep looping.
16    # Greater than 10. STOP!