Question

I have SQL table with a column with a data type of Float. There is an external app that writes percentage values to this column and I read them and display them in a web app.

I understand how to convert decimal’s to percentages; usually I would multiply by 100, but this is a little different.

The values in the DB look like this:

 0.95  <-- DB  5%  <-- UI
 0.85  <-- DB  15% <-- UI
 0.5   <-- DB  50% <-- UI

I have tried

number * percentage / 100

and

((percentage /100) * value).ToString();

and

 string percentage = string.Format("Percentage is {0:0.0%}", value);

and

 percentage/100m*value

and

 myDecimal.ToString("0.00");

and finally, what I thought was close:

Math.Round(myDecimal, 2).ToString("{0.00}");

and of course various string formatting things like

 MyDecimal.ToString("P"), .ToString("P1"), etc)

Articles on Formatting, Rounding and Converting Percentages in C#:

Convert percentage to nearest fraction,
Working percentage in c#,
http://www.dotnetperls.com/percentage,

But I can not for the life of me find a math calculation or built in c# conversion to give me the output I need.

What it seems like I need to do is get the 0.96 digits to be subtracted by some number and then in turn multiply that by 100, but the 0.5 being 50% always throws my math off….

This seems like it would be a common conversion; what I am missing here?

UPDATE

Here is a the solution I ended up with, which works great! (Thanks Reed)

            var li = new List<Object>();
        var retVal = new List<string>();

        li.Add(.5);       // 50%
        li.Add(.95);      // 95%
        li.Add(.85);      // 85%
        li.Add(0.87813);  // 12.18700%

        foreach (var o in li)
        {
            var value = Convert.ToDouble(o);
            string percentage = string.Format("Percentage is {0:0.0%}", 1.0 - value);

            retVal.Add(percentage);
        }

LINKS

For the sake of completeness, here is a pretty consise list of resources on Decimals, Percentages, Doubles, and conversions in C#:

A+

Working percentage in c#
Format decimal for percentage values?
Convert percentage to nearest fraction
http://www.dotnetperls.com/percentage
.NET: Decimal to rounded string
C# Is there a built-in function to convert a formatted String back to a Number?

A-

Format decimal as a percent with specific decimal places
Convert decimal to percent or shift decimal places. How
How to convert percentage string to double?

B+

two ways of displaying a decimal
http://msdn.microsoft.com/en-us/library/dwhawy9k.aspx

Answer 1

I believe you’d want:

string percentage = string.Format("Percentage is {0:0.0%}", 1.0 - value);

If you just want the number:

string percentage = (1.0 - value).ToString("P");

Or, the number without decimal precision:

string percentage = (1.0 - value).ToString("P0");