Bringing a big number to a small normalized number

What's wrong with:

double l = Math.Ceiling(Math.Log10(number));
double n = number / Math.Pow(10,l-1);
label1.Text = Math.Round(n,3).ToString();

?

Note (if needed) you have to handle as special cases the powers of ten (e.g. 10, 100, 1000).

Hello,
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Allso I sugest that you simplify code :

Use variable type of double for value of "Convert.ToDouble(s)" because it is too complex inside Math.Round()
Sometimes this statment

for(int i=0;i<=s.Length-1;i++)

won't work correct ( I still didn't find out why ) so I use

for(int i=0;i<=s.Length-1;i=i+1)

And you have error in selecting type of int for variable norm, it should be type of double because int type is too small for a range of numbers that may appear during the work of program.
Avoid variable declaration in the same command that you use in the program,
exmpl :

for(int i=0;i<=s.Length-1;i++)

You allso have error in condition
for stopping the for..next loop, it should be i < s.Lenght-1

I have changed your code so now it gives this result for your example 18668951 to 1,867 or 11256,125698 to 1,126 and it should be like that.

It looks like this :

void Button1Click(object sender, EventArgs e)
{
    //
    // Declaration of variables
    //
    string s = "";
    double norm = 0;
    double number = 0;
    double s1 = 0;
    int i = 0;
    int lenght = 0;

        s = textBox1.Text;
        number = Convert.ToDouble(s);
        s1 = Math.Round(number,3)*1000;
        lenght = s1.ToString().Length;
        norm=1;
        for(i=0;i<lenght-1;i=i+1)
        {
            norm = norm * 10;
        }
        label1.Text =Math.Round((s1/norm),3).ToString() ;
}

You should allso take care of relevance of entered number , if it is not number at all Convert.ToDouble(s) won't work.






Al the best
Perić Željko

Since you are just reformating a string you may could use:

string strNormalized = String.Format("{0:E}", Double.Parse(strNumberInTextBox));

But I think you don't want to show the exponent?
A possible function could be defined like this (others showed it)

public static string GetNormalizedString(string strValue)
        {
            double dValue = Double.Parse(strValue, CultureInfo.InvariantCulture); // If you are not shure strValue is a double, use TryParse instead

            // 1. Get the "magnitude" of our number
            double dLog = Math.Floor(Math.Log10(dValue));
            // 2. Divide through the found magnitude
            double dResult = dValue / Math.Pow(10, dLog);

            // (Re-)format the result - in this case with rounding - maybe you just want to cut the value - leave Math.Round call away
            return String.Format("{0:F3}", Math.Round(dResult, 3));
        }

Attention: In the code you showed you do some not needed string conversions (bad performance). And think about what you do with the converted value later in your app, because you are loosing precision (maybe you want to hold the "real" value in a seperate variable for later use in calculations...)