How do you declare a constant in programming?

To declare a constant in programming, the correct method involves using a specific keyword, such as "const", which denotes that the variable's value cannot be reassigned after its initial definition. This ensures that the constant remains fixed throughout its scope, providing reliability and maintaining intended behavior in the code.

When you use "const" in languages like JavaScript or C++, it informs the compiler and the programmer that the variable should not change, which can prevent errors that stem from unintentional modifications of values. This immutability is crucial in many programming scenarios where certain values must remain constant to ensure the integrity of operations or algorithms.

This approach differs significantly from the other options, which may suggest allowing reassignment, declaring scope limitations without guaranteeing constancy, or not assigning any value at all, which does not fulfill the requirement of declaring a constant. The essence of declaring a constant lies in its protected nature against reassignment, hence the use of "const" or similar keywords in other programming languages.