You cannot change the type for a var-type variable.
using System;
class Program
{
static void Main(string[] args)
{
var i = 5;
i = "rntsoft.com";
}
}
The code above has the following error message:
C:\g>csc Program.cs
Microsoft (R) Visual C# 2010 Compiler version 4.0.30319.1
Copyright (C) Microsoft Corporation. All rights reserved.
Program.cs(8,13): error CS0029: Cannot implicitly convert type 'string' to 'int'