What is an advantage and disadvantage of a constant in programming?

Answer 1

A constant is simply a variable (or object) that does not change value from the user's point of view. By notifying the language compiler that a value is not meant to be changed, the compiler will allocate that value to static memory, regardless of where that constant is physically declared in your source code (whether at global scope, file scope, class scope, function scope or local scope). Moreover, if you have more than one constant of the same type and value, the compiler will allocate only one instance of that value, thus saving memory.

The disadvantage to constants is largely a result of misuse. For instance, programmers are notorious for wanting to keep all constants in the same place (such as a constants.h file in C or a static class in C++). However, this is rarely a good idea given that any decent compiler will put all constants in the same place anyway; in static memory. Declaring constants as and when they are actually required makes code much easier to read and maintain because the value is right there in the code itself; you don't have to go looking it up.