Find trailing zero of n factorial

Hello,

Here is small logic program to find trailing zero in n factorial. (n > 0). Here we are dividing the passing parameter with power of 5.

e.g .  Take 51.   How many trailing zero for 51 factorial. Let’s start. 

          Now Take 5  and divide 51 with 5 will ans. = 51/5 = 10  let  save  10 in variable.

          Now increase power of 5 = 5²  = 25 and divide 51 with 25 = 51/25 = 2.

         Add ans in previous answer 10+2 = 12

         Now increase power of 5 = 5³ = 125.  Now check 51/124  < 0.

         so it is not possible more to divide 51.

          So  your answer  = 12

Here is C# implementation for this logic.

        public static double ZeroCnt(int num)

        {

            int cnt, pow, number;

            cnt = 0;

            pow = 1;

            number = 5;

            while (number < num)

            {             

                cnt +=  num / number;

                pow ++;

                number = Convert.ToInt32(Math.Pow(5, pow));

            }

            return cnt;

        }