First of all, we need to understand the usage of both variables and constants. Variables are used to store values which can be changed in run time whereas constant cannot be changed.

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So, both "Variable" and "Constant" come under a concept called "Identifiers". As the name suggests, identifiers help us to identify a value which is stored in the memory with the help of a name. It's like a box which contains some values/information with a label attached.

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Also Also identifiers can be function names, type names, class names, labels, etc.,can be function names, type names, class names, labels, etc.,

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It totally makes no sense. This statement states that a CONSTANT is a VARIABLE but it's value can't be changed. If CONSTANT is a VARIABLE then the value can be changed. A total collapse in the meaning.

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Say if you wanna store a number "42" in your program/code, you can assign it to an identifier. So that you can use it later in your program.

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If a value stored in an identifier which can be changed in the run time, it is called a "Variable". If it cannot be changed it is called a "Constant".

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Variables and Constants are mostly misunderstood in programming. Most of the time, most of the people read bad definitions on Constants. A thread on this.