Nullable With Math.Abs() Method

Question

The following nullable decimal code fired Overload Method Error:

decimal? t1 = null;
decimal? t2 = null;
decimal? t3 = null;
decimal res = 0;
decimal tt1 = 0;
decimal tt2 = 0;
decimal tt3 = 0;

if (decimal.TryParse(textBox1.Text, out tt1))
    t1 = tt1;
if (decimal.TryParse(textBox2.Text, out tt2))
    t2 = tt2;
if (decimal.TryParse(textBox3.Text, out tt3))
    t3 = tt3;
res = Math.Abs(t1 + t2 - t3);
textBox4.Text = res.ToString();

The above code suggested calculation between three textBoxes and fourth textBox showing result of them. But the problem is Math.Abs method is not supported for nullable type decimal. How to overcome?. How to overcome means i wants to allow nullable in Math.Abs method by another way.

Answer 1

You should perform null checks, but the code would be:

res = Math.Abs((decimal)t1 + (decimal)t2 - (decimal)t3);

Or:

res = Math.Abs(t1.Value + t2.Value - t3.Value);

Answer 2

My guess is that you actually want Math.Abs(tt1 + tt2 - tt3) anyway.

If you actually want null to be returned if any of the inputs are null, then maybe you want something like this:

    decimal? res = t1 + t2 - t3;
    if (res != null)
        res = Math.Abs(res.Value);
    textBox4.Text = res.ToString();

Answer 3

How about something like this?

     decimal? a = 4;
     decimal? b = 3.254m;
     decimal? c = 9.765675m;

     decimal? d = (a + b - c);

     decimal? res = null;
     if (d != null)
     {
        res = Math.Abs((decimal)d);
     }
     textBox4.Text = (res != null) ? res.ToString() : "null";

Answer 4

Having reread your example more closely, I assume it was intended to be a contrived example, since the only reason you would have set t1, t2 or t3 was to give the opportunity of demonstrating the problem. I have therefore reworked my example to something that is hopefully more in keeping with your intent.

    private void button1_Click(object sender, EventArgs e)
    {
        //Read some values in a contrived example to get a mixture of null 
        //and not null values into t1, t2 & t3
        decimal? t1 = null;
        decimal? t2 = null;
        decimal? t3 = null;
        decimal res = 0;
        decimal tt1 = 0;
        decimal tt2 = 0;
        decimal tt3 = 0;


        if (decimal.TryParse(textBox1.Text, out tt1))
            t1 = tt1;
        if (decimal.TryParse(textBox2.Text, out tt2))
            t2 = tt2;
        if (decimal.TryParse(textBox3.Text, out tt3))
            t3 = tt3;

        //We have setup our inputs now, so lets get down to how to handle the problem                    
        //now.  This should probably be in a separate function, but we are in a _Click 
        //method, so I am assuming we are overlooking such things in this example...

        //return without setting textBox4 if any of t1, t2 & t3 are null
        if (!t1.HasValue || !t2.HasValue || !t2.HasValue)
        {
            return;
        }           
        //1, 2 & 3 are all valid, so set textBox4
        res = Math.Abs(t1.Value + t2.Value - t3.Value);
        textBox4.Text = res.ToString();
   }

The main points here are we should be explicit that textBox4 is not set when any of the 3 inputs are null, rather than inferring this from the return from Math.Abs(), and also to use the Value property on the nullable type rather than casting to the value type, which I just prefer stylistically..

Answer 5

What result do you expect if you pass null into Math.Abs? But you might want to use the null coalescence operator ??.

res = Math.Abs(()??0);

where the value after ?? is the alternate value used if the expression before it is null. So you want to get null if the argument to Abs is null?

Decimal? temp=t1 + t2 - t3;
if(temp!=null)
    temp=Math.Abs(temp.Value);
textBox4.Text = temp.ToString();

Answer 6

The Exact Solution For Above Problem is :-

private void button1_Click(object sender, EventArgs e)
    {
        decimal? t1 = null;
        decimal? t2 = null;
        decimal? t3 = null;
        decimal tt1 = 0;
        decimal tt2 = 0;
        decimal tt3 = 0;

        if (decimal.TryParse(textBox1.Text, out tt1))
            t1 = tt1;
        if (decimal.TryParse(textBox2.Text, out tt2))
            t2 = tt2;
        if (decimal.TryParse(textBox3.Text, out tt3))
            t3 = tt3;

        decimal? res = t1 + t2 - t3;
        if (res != null) 
        {
            res = Math.Abs((decimal) res);
        }

        textBox4.Text = res.ToString();
      }

See This code doesn't throw any error and clear the nullable problem on use of Math.Abs() Method.