What is the difference between Convert.ToInt32 and (int)?

Question

The following code throws an compile-time error like

Cannot convert type \'string\' to \'int\'

string name = Session[\"name1\"].ToString();
int i = (         


        

Answer 1

You're talking about a C# casting operation vs .NET Conversion utilities

• C# Language-level casting uses parenthesis - e.g. (int) - and conversion support for it is limited, relying on implicit compatibility between the types, or explicitly defined instructions by the developer via conversion operators.
• Many conversion methods exist in the .NET Framework, e.g. System.Convert, to allow conversion between same or disparate data types.

(Casting) syntax works on numeric data types, and also on "compatible" data types. Compatible means data types for which there is a relationship established through inheritance (i.e. base/derived classes) or through implementation (i.e. interfaces).

Casting can also work between disparate data types that have conversion operators defined.

The System.Convert class on the other hand is one of many available mechanisms to convert things in the general sense; it contains logic to convert between disparate, known, data types that can be logically changed from one form into another.

Conversion even covers some of the same ground as casting by allowing conversion between similar data types.

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Remember that the C# language has its own way of doing some things.
And the underlying .NET Framework has its own way of doing things, apart from any programming language.
(Sometimes they overlap in their intentions.)

Think of casting as a C# language-level feature that is more limited in nature, and conversion via the System.Convert class as one of many available mechanisms in the .NET framework to convert values between different kinds.