Some variables don’t change value during the execution of a program. These variables are constants that appear many times in your code.
The rules for naming variables also apply to naming constants. The constant’s value is a literal value or a simple expression composed of numeric or string constants and operators. You can’t use functions in declaring constants.
Const pi As Double = 3.14159265358979 Console.WriteLine(pi)
Whenever you changed this variable, it will give you error.