C#: How to cast a value from a database field to an explicit typed variable

2018-10-11 18:57 Valeriy imported from Stackoverflow

In fact, I've already found the answer to my question, here at stackoverflow. But because of my low reputation, I can't give thank to the person (Richard Petheram) who gave me the hint. So please add me the votes to 15 so I could at least thank helping people. Thanks in advance )

Here is the question and the answer helped me

and here is my function

    public static T NvlO<T>(object a, T b)
    {
        if (a == null)
            return b;
        else
        {
            var lSrcType = a.GetType();
            var lDestType = typeof(T);

            if (lDestType.IsValueType && lDestType.IsAssignableFrom(lSrcType))
                return (T)a;
            var lDestTC = TypeDescriptor.GetConverter(typeof(T));
            if (lDestTC.CanConvertFrom(lSrcType))
                return (T)lDestTC.ConvertFrom(a);
            else
            {
                var lSrcTC = TypeDescriptor.GetConverter(lSrcType);
                String lTmp = lSrcTC.ConvertToInvariantString(a);
                return (T)lDestTC.ConvertFromInvariantString(lTmp);
            }
        }
    }

example of using

long _userID = Utils.NvlO(dr["UserID"], 0);

and if you think that the function does not match the correct programming patterns, write why you think so.

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"Cannot convert from string to double"

Please can someone help me with the following problem. In the last line I get an error message stating that I

cannot convert from string to double

It works though in the first two lines. Help will be much appreciated.

DeltaY.Text = (Convert.ToDecimal(YCrd2.Text) - Convert.ToDecimal(YCrd1.Text)).ToString();

DeltaX.Text = (Convert.ToDecimal(XCrd2.Text) - Convert.ToDecimal(XCrd1.Text)).ToString();

Obs1Angle.Text = Math.Tan((Convert.ToDecimal(DeltaY.Text)) /
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Difference between double and float in floating point accuracy
After reading this question, and this msdn blog, I have tried few examples to test this:
```
Console.WriteLine(0.8-0.7 == 0.1);
```
And yes, the expected output is False. Hence I try cast the expression in both side to double and float to see whether I can get a different result:
```
Console.WriteLine((float)(0.8-0.7) == (float)(0.1));
Console.WriteLine((double)(0.8-0.7) == (double)(0.1));
```
The first line output True but the second line output False, why is this happening?

Furthermore,
```
Console.WriteLine(8-0.7 == 7.3);
Console.WriteLine(8.0-0.7 == 7.3);
```
Both of the line above give True even without casting. And ...
```
Console.WriteLine(18.01-0.7 == 17.31);
```
This line output False. How is subtracting 8 difference from subtracting 18.01 if they both are subtracted by a floating point number?

I've tried to read through the blog and question, I can't seem to find answer else where. Can someone please explain to me why are all of these happening in Layman's language? Thank you in advance.

EDIT:
```
Console.WriteLine(8.001-0.001 == 8); //this return false
Console.WriteLine(8.01-0.01 == 8); //this return true
```
Note: I am using .NET fiddle online c# compiler.
Style View diffrent for Desktop and Mobile | asp.net core 2 mvc5
So I have been doing c# / razor web applications in asp.net core 2 with mvc 5 and got along with it well but now I need to make a new Website which is capable of responsive design.

I baisicly just need to change my view and its css depending on the device the user is on. Im using bootstrap already which does some part of that job already but I just want to style my view diffrently.

Ive gone through loads of turtorials already but all of them arent in asp.net core 2 and use BundleConfigs ect. I havent found a turtorial or template for my framework and version.

This is baisicly just something im looking for and just pseudo code: this is supposed to be a example of the full view. So obviously not an if else for every button.
```
if(device==mobile){
<a class="btn btn-sm">Link</a>
}
else{
<a class="btn btn-lg">Link</a>
}
```
I know that this isnt the perfect question for stackoverflow since im just looking for help and I apologise but im just seraching for either small help or a linked turtorial or something.

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C#: How to cast a value from a database field to an explicit typed variable

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