Why do i need to wrap this code in a cast to short?

If i have some code like the following:

short 开发者_高级运维myShortA = 54;
short myShortB = 12;
short myShortC = (short)(myShortA - myShortB);

Both operands are shorts and it's going into a short so why do i have to cast it?

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Because there's no "short - short" operator. Both operands are promoted to int.

From section 7.7.5 of the C# 3 spec:

The predefined subtraction operators are listed below. The operators all subtract y from x.

• Integer subtraction:

  int operator –(int x, int y);
  uint operator –(uint x, uint y);
  long operator –(long x, long y); 
  ulong operator –(ulong x, ulong y);
  

  In a checked context, if the difference is outside the range of the result type, a System.OverflowException is thrown.

(And then there's floating point subtraction.)

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To make things a little bit easier, you could simply write an extension method like this:

public static class NumericExtensions
{
    public static short Subtract(this short target, short value)
    {
        return (short)(target - value);
    }
}

Others have answered your question... :)