Trailing Zeros

Challenge

Write a function called countTrailingZeros (int X) that determines the number of trailing zeros at the end of X! (X factorial), where X is an arbitrary input from the user.

Note: In case of a negative number X, your program should return -1.

Example 1

Input: 12

12! = 479001600

Number of zeros at the end of 12! = 2

Example 2

Input: 5

5! = 120

Number of zeros at the end of 5! = 1

Example 3

Input: -20

Number of zeros at the end of -20! = -1

Coding exercise

Try to solve this challenge on your own. If you can’t solve it, you can look at the solution and explanation below.