7.2.2 LIFO and FIFO stack operations As already mentioned, the stack is a linear list of strings. Obviously, this list has two ends. Strings can only be extracted from one end, while strings can be added to both ends. If a set of new strings are added to the same end as they are later extracted from, the strings will be extracted in the reversed order with respect to the order in which they were added. This is called stacking “LIFO”, which means “last-in-first-out”, meaning that the last string stacked, will be the first string extracted, i.e. reversal of the order. Similarly, when a set of strings are stacked in the end opposite to the end which they are later extracted from, they will be extracted in the same order in which they were stacked. This is referred to as “FIFO” stacking, meaning “first-in-first-out”. The FIFO method of stacking is also sometimes referred to as “queueing”, while the LIFO method is sometimes referred to as “stacking” or “pushing”.