What is a primary characteristic of constant variables in programming?

Constant variables are defined by their immutability; once they are assigned a value during their definition, that value cannot be altered throughout the program. This characteristic is crucial in programming because it helps maintain the integrity of data that should remain unchanged, thereby preventing accidental modifications that could lead to errors or unintended behavior in the application.

For example, using constant variables for values like mathematical constants (such as pi) or configuration settings allows programmers to ensure that these critical values remain consistent and reliable throughout the code.

While constant variables do have a specific type (which relates to the second option), it is the inability to change their value after initial assignment that fundamentally defines them. This immutability makes them distinct from regular variables, which can be modified at any time during runtime. Temporary storage, mentioned in the fourth option, is also not applicable; constant variables are intended for values meant to remain constant over the program's execution rather than for transient values.