#204 – Three Rules About Using Implicitly-Typed Variables

You can create an implicitly-typed variable using the var keyword.  The type is inferred, rather than declared.

Here are a few additional rules about using implicitly-typed variables.

Rule #1 - You can use var only for local variables

You can’t use var when declaring class fields/properties.

    public class Person
    {
        public var Height;    // Compile-time error
    }

Rule #2 - You must initialize an implicitly-typed variable when you declare it

If you don’t initialize an implicitly-typed variable, the compiler can’t infer the type.

        static void Main()
        {
            var height;   // Error: Implicitly-typed local variables must be initialized
        }

Rule #3 - You must declare implicitly-typed variables one at a time

You can’t declare more than one variable on the same line with var.

        static void Main()
        {
            int i, j, k;   // Declare three int variables

            var x, y, z;   // Error: Implicitly-typed local variables cannot have multiple declarators
        }