Reduce one from absolute value?

Question

I have an integer that needs its absolute value to be reduced by one.

Is there a shorter way than this:

if(number > 0) number--; else if (number < 0) number++;

Answer 1

Even shorter:

number -= Math.Sign(number);

Math.Sign returns -1, 0, or 1 depending on the sign of the specified value.

Extension Method

Since you say you face this situation a lot it might be beneficial to make this an extension method to better express your intent:

public static int ReduceFromAbsoluteValue(this int number, int reduceValue)
{
    return number - Math.Sign(number) * reduceValue;
}

4.ReduceFromAbsoluteValue(1);  // 3
-4.ReduceFromAbsoluteValue(1); // -3
0.ReduceFromAbsoluteValue(1);  // 0

Alternatively name this AddToAbsoluteValue and change it to add the value.