1. Difference between a variable and a constant
A variable is what, that you can change it's content later in you code
A constant is what you try to change, you can’t because a content is something
that's can't change.
The constants value is locked for the duration of the program.
But the variable value is not locked for the duration of the program.
There are no basic kinds of Constant in program.
There are two basic kinds of variables in program which are numeric and
character.
PI (π) for instance is a good example to declare as a constant.
0-9,A-Z etc symbol can be used as example for variable.