How can I manipulate specific digits of an integer value?

Question

I have to create a control that can manipulate each "digit" of an integer value ( from 0 to 999,999 ).

I know how to "Get" a digit of the integer - just Mod/Div -

public class IntegerModel{
    private int _value = 0;
    private int _GetValue( int baseValue, int modBy, int divBy ) => 
        ( baseValue % modBy ) / divBy;

    public int Value => _this.Value;

    public One => {
        get => this._GetValue( this.Value, 10, 1 );
        set => Console.WriteLine( "What do I put here?" );
    }

    public Ten{
        get => this._GetValue( this.Value, 100, 10 );
        set => Console.WriteLine( "What do I put here?" );
    }
}

The problem is that I don't know how to eloquently SET the digit value.

If I was working in Binary it would be as simple as using some bitwise operators ( it may still be but I don't know exactly how to do it ).

So, ideally, if I were to, using this class, do the following, I would get the given output.

IntegerModel Foo = new IntegerModel( );
Foo.One = 7;
Foo.Ten = 3;
Console.WriteLine( Foo.Value ); //Output should be 37

What would I need to put in the One and Ten property setters to be able to achieve the desired behavior?

Can't you store array of digits, instead of one number? It would be much easier to manipulate with one digit. — Yurii N., Sep 25 '17 at 14:27

Dmitry Bychenko · Accepted Answer · 2017-09-26T09:09:16.053

3

I suggest modular arithmetics for both set and get; another suggestion is to implement indexer in order to access n-th digit of the integer.

  public class IntegerModel {
    private int _value = 0;

    private static int Power10(int value) {
      return (int) Math.Pow(10, value);
    }

    public int Value {
      get {
        return _value;
      }
    }

    //TODO: Implement ToString, Equals etc.

    public int this[int index] {
      get {
        if (index < 0 || index > 6)
          throw new ArgumentOutOfRangeException("index");

        return (_value / Power10(index)) % 10;  
      }
      set {
        if (index < 0 || index > 6)
          throw new ArgumentOutOfRangeException("index");
        else if (value < 0 || value > 9)
          throw new ArgumentOutOfRangeException("value");

        _value = (index / Power10(index + 1)) * Power10(index + 1) + 
                  value * Power10(index) +
                 _value % Power10(index);
      }
    }
  }

If you insist on One, Ten etc. properties you can easily add them:

  public int One {
    get {return this[0];}    // 0th digit
    set {this[0] = value;}   // 0th digit
  }

  public int Ten {
    get {return this[1];}    // 1st digit
    set {this[1] = value;}   // 1st digit
  }

  public int Hundred {
    get {return this[2];}    // 2nd digit
    set {this[2] = value;}   // 2nd digit 
  }

Test:

  IntegerModel test = new IntegerModel();

  // 987:
  test[0] = 7; // Last   (0th digit from the end)
  test[1] = 8; // Middle (1st digit from the end)
  test[2] = 9; // First  (2nd digit from the end)

  // 987
  Console.WriteLine(test.Value);

edited Sep 26 '17 at 09:09

answered Sep 25 '17 at 14:27

Dmitry Bychenko

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I like the look of this. I will try it out. – Will Sep 25 '17 at 14:39
Also, the reason for `One`, `Ten`, etc. is because the class is going to serve as a Model for an interface. – Will Sep 25 '17 at 14:50
@Will: interface with indexer seems to be a better choice; however, if the interface is fixed and you can't change it, well, `One` and `Ten` should be implemented. – Dmitry Bychenko Sep 25 '17 at 14:55
Problem is it has to support bi-directional binding. Well, it should in my MIND anyway... Interface hasn't been written yet. And you can't call `OnPropertyChanged` with an indexer. At least, you can't to my knowledge but that goes beyond the scope of this question. – Will Sep 25 '17 at 15:00
Tested. Works. Genius in simplicity. Here's your imaginary internet points. – Will Sep 25 '17 at 15:15
One thing - Setting the value works fine, getting it does not. I think that the error is in the return of the indexed getter - rather than saying `return ( index / ... )`, I think it should be saying `return ( this.Value / ... )` – Will Sep 25 '17 at 17:22
@Will: I am very sorry for the typo, `_value` for sure, not `index`. I've edited the answer. – Dmitry Bychenko Sep 25 '17 at 19:05

score 0 · Answer 2 · answered Sep 25 '17 at 14:26

1 Split your overall value into three sections - high, low, relevant digit. Discard relevant digit...I just mentioned it to indicate the gap between "high" and "low"

2 To get hi, divide by something like (10^position + 1), then multiply by 10^(position + 1)

3 multiply relevant digit by (10^position)

4 add that to low (low should now be one digit longer)

5 Add high to low to get your final answer

My math is terrible, so expect a lot of off-by-one. I'm pretty sure the logic is sound, though.

How can I manipulate specific digits of an integer value?

2 Answers2