删除双精度的最后一个十进制值

Question

I am making a calculator in C#. I save the input from the user as a double.

I use the following code to delete the last entered number in a double withour decimals.

i = (i - (i % 10)) / 10;

This wil delete the last number.

12345 wil become 1234

What I can't figuere out is how to make this happen for decimal values.

2134.765 must become 2134.76

my program uses a var to see if a point has been put in so I only need the math to delete the last number.

Answer 1

Since you're dealing with character input and not math yet, just keep your input as a string until you need to perform an operation on it . Then removing the last character is as simple as

input = input.Substring(0,input.Length-1);

Otherwise you have to deal with ambiguous situations like:

• What if the last character is a decimal point?
• What if one or more trailing zeros have been entered?
• Has a decimal point been entered (you say you already track this)

Answer 2

The easiest way would probably be to use your own number format - you want to keep the values decimal anyway. double is a terrible choice for that. At the very least, use a decimal so that you're guaranteed the decimal representation of the number.

Answer 3

If you really always only wanna delete the last digit in the number I would use a trick and convert the number to string remove the last char and back.

var number = 123,456;
var strNumber = number;
strNumber.Remove(strNumber.Length - 1);
number = double.parse(strNumber);