Best practice for casting in c sharp

You have two different things.

// 1. a cast
int MyInt = (int)SomeVariable;

SomeVariable needs to be a type that can directly cast to an integer, i.e. a numeric, character or byte which is or has an integral part. Casting from float or double means you lose the fractional part, but that is useful at times.

// 2. converter
int MyInt = Convert.ToInt32(SomeVariable);

In this case you are taking a value which cannot be directly referenced as a number (e.g. a string such as "1378") and parsing it into its constituent parts and converting to the value it represents.

You can also use Int32.TryParse which allows you to convert if it's possible, and return a bool indicating success/failure.

Best, absolutely the best practice is no casting at all! In many cases, it's possible to design code without type cases. Use generics, in particular.

However, in some cases, type casting is unavoidable. Sometimes even dynamic casting using "as" is needed, but this is often a sign of OOP abuse. You did not ask about it, but it's important to know:
http://msdn.microsoft.com/en-us/library/cscsdfbt%28v=VS.100%29.aspx[^].

See also http://msdn.microsoft.com/en-us/library/scekt9xw.aspx[^].

As to "Convert", to me, this is often a sign of lack of understanding (even when it works correctly). A cast is not conversion, a conversion is not a cast. A "classic" cast like (int)… is better, but not always applicable. In your case, it is probably not. If the input is string, it's much better to use Parse or TryParse, as it reflects the essence of what's actually done.

The cast like (int)… is mostly uses to cast downcasting (http://en.wikipedia.org/wiki/Downcasting[^], note the danger of it) and casting to a narrower type like int to short, int to byte, etc. In all cases, casting can fail, should be used with care. More exactly, it should be uses mostly when you can know in advance that the case is successful.

—SA

Have a look at this question on MSDN

http://social.msdn.microsoft.com/Forums/en-US/netfxbcl/thread/1ca53a60-e094-4073-ab33-27cca0bdbad4/[^]

* (int) will only convert types that can be represented as an integer.

So, you can't always use the (int) syntax. Depending on what you are trying to cast, Convert.ToInt32 or Int32.TryParse might be the option you need.

Convert.ToInt32 is better.

Best Practice for casting is Convert.ToInt32 compare to (int)

Because if result value is null in case of (int) casting it will throw exception.

But in case of Convert.ToInt32 if resulting value is null, it gives result. doesn't throw exception.