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The two main operations applicable to a stack are:
Some environments that rely heavily on stacks may provide additional operations, for example:
Stacks are either visualised growing from the bottom up (like real-world stacks) or growing from left to right, so that "topmost" becomes "rightmost". This means that a right rotate will move the first element to the third position, the second to the first and the third to the second. Here are two equivalent visualisations of this process:
apple banana banana ==right rotate==> cucumber cucumber apple
cucumber banana apple ==right rotate==> apple cucumber banana
A stack may be represented in computers inside block of memory cells, with the bottom at a fixed location, and a variable stack pointer to the current top cell. pushing first increases the top pointer by one, pointing it to the next cell, and then fills that with the new top value. poping first takes the top value, and then decreases the top pointer by one. Increasing and decreasing may be exchanged to yield a stack representation that grows from high addresses to lower ones.
Many CPUs have registers that can be used as stack pointers. Some, like the x86, have special instructions that implicitly use a register dedicated the job of being a stack pointer. Others, like the PDP-11 and the 68000 family have addressing modes that make it possible to use any of a set of registers as a stack pointer.
Calculators employing reverse polish notation use a stack structure to hold values.
A number of computer languages are stack-oriented, meaning they define most basic operations (adding two numbers, printing a character) as taking their arguments from the stack, and placing any return values back on the stack. For example, PostScript has a return stack and an operand stack, and also has a graphics state stack and a dictionary stack.
The Forth language uses two stacks, one for argument passing and one for subroutine return addresses. The use of a return stack is extremely commonplace, but the somewhat unusual use of an argument stack for a human-readable programming language is the reason Forth is referred to as a stack-based language.
Almost all computer environments use a stack to hold information about procedure/function nesting.