How to convert from big number to short plus Exp?-CodePudding

Maybe I just didn't sleep enough today and can't think clearly enough today:

I have big numbers, and I have an array of Exp "big number names". I want to get the Exponent of the big number and then display the big number as a decimal value big number label.

string[] exponent = 
    {
        "Mil",
        "Bil",
        "Tri",
        "Qua",
        "Qui",
        "Sex",
        "Sep",
        "Oct",
        "Non",
    };

double value = 1230000000;
if(value > 1000000)
{
  int pow = (int)(value / 1000000);
  res = value.ToString("#.##")   exponent[pow] ;
}

Expected output I want would be:

1.23Bil

but I'm clearly not converting value correctly.

CodePudding user response：

Using the logarithm base 10 will get you the nearest power of 10 to the number, but you need to round to the nearest multiple of 3 of the power of ten (you really want the log base 1000).

Then you need to divide the value by that power of 1000 to get the matching mantissa:

string res;
if(value >= 1e6) {
  int pow = ((int)Math.Log10(value))/3;
  res = (value/Math.Pow(10, 3*pow)).Dump().ToString("#.##")   exponent[pow-2] ;
}
else
    res = value.ToString();