Round any n-digit number to (n-1) zero-digits

Question

Sorry hard to formulate.

I need to round like this:

12 -> 10
152 -> 200
1538 -> 2000
25000 -> 30000
etc. 

Twisting my head, but can't see how to make this. Must work for any n number of digits. Anyone got an elegant method for it?

c# or vb.net

Answer 1

How about this:

        double num = 152;

        int pow = (int)Math.Log10(num);

        int factor = (int)Math.Pow(10, pow);

        double temp = num / factor;

        double result = Math.Round(temp) * factor;

Answer 2

I think you should try with something like this:

public int Round( int number)
{
    int power = number.ToString().Length - 1;
    int sz = Math.Pow(10, power);

    int rounded = (int)Math.Round( number / sz );

    return rounded * sz;
}

The idea is to get the size of the nearest 10 power, available by the length of the number expressed as a string. Then divide the number by that power, leaving it like 1,2 and then round it using the Math.Round method and restore the size by remultiplying it to the power.

Much like the previous answer...