What is the main function of a stack?

The main function of a stack is to follow the Last In First Out (LIFO) principle, which dictates that the last element added to the stack will be the first one to be removed. This structure is akin to a stack of plates where you can only add or remove the top plate. When you push an element onto a stack, it goes on top, and when you pop an element, the topmost element is removed first. This characteristic makes stacks particularly useful in scenarios where you need to reverse an operation or manage function calls (like in recursion) where the most recently called function must complete before returning to previous functions.

In contrast, the other options highlight different characteristics: random access would imply a structure like an array, adding and removing from the front suggests a queue, and mapping keys to values is a feature of data structures like hash tables or dictionaries. These features do not align with the primary and defining function of a stack, which is strictly based on the LIFO order of operations.