Calculating VAT backwards always returns as 0 in c#

public string s()
{ 
  d开发者_如何学编程ouble price = 123.12
  double preVatPrice = (100 / (100 + 20) + price);

  return preVatPrice.ToString();
}

in c# this always returns as '0' any ideas why?

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This is integer division:

100 / (100 + 20)

That will result in a 0.

Make it into:

100.0 / (100.0 + 20.0)

To ensure all parameters are floating point types.

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BTW - the function returns "123.12" when I test it.

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Update:

As pointed out in several comments - you should be using decimal for monetary calculations, though in this case it is unlikely to be a problem.

The Decimal value type is appropriate for financial calculations requiring large numbers of significant integral and fractional digits and no round-off errors.

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Some of your literals are ints, use (100.0 / (100.0 + 20.0) + price) to get double precision arithmetic.

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double preVatPrice = ((double)100 / (100 + 20) + price);