Question 14

What is the output of the following code?

ans, count = 0, 0
while count < 4:
    ans = (ans + count) * (-1)**count
    count += 1

print(ans)

Solution

Given ans = 0 and count = 0 from the start,

count < 4?	ans = (ans + count) * (-1)**count
0 < 4 (True)	(0 + 0) * (-1)**0 = 0 * 1 = 0
1 < 4 (True)	(0 + 1) * (-1)**1 = 1 * (-1) = -1
2 < 4 (True)	(-1 + 2) * (-1)**2 = 1 * 1 = 1
3 < 4 (True)	(1 + 3) * (-1)**3 = 4 * (-1) = -4
4 < 4 (False)	Final ans = -4

Answer

-4