When to use a Cast or Convert

Cast when it's really a type of int, Convert when it's not an int but you want it to become one.

For example int i = (int)o; when you know o is an int

int i = Convert.ToInt32("123") because "123" is not an int, it's a string representation of an int.

See Diff Between Cast and Convert on another forum

Answer

The Convert.ToInt32(String, IFormatProvider) underneath calls the Int32.Parse (read remarks).
So the only difference is that if a null string is passed it returns 0, whereas Int32.Parse throws an ArgumentNullException.
It is really a matter of choice whichever you use.

Personally, I use neither, and tend to use the TryParse functions (e.g. System.Int32.TryParse()).

UPDATE

Link on top is broken, see this answer on StackOverflow.

There is another difference. "Convert" is always overflow-checked, while "cast" maybe, depending on your Settings and the "checked" or "unchecked" keyword used.

To be more explicit. Consider the code:

int source = 260;
byte destination = (byte)source;

Then destination will be 4 without a warning.

But:

int source = 260;
byte destination = Convert.ToByte(source);

will give you a exception.