Problem Statement

A stack is a container of elements with   last in, first out   access policy.   Sometimes it also called LIFO. The stack is accessed through its top. The basic stack operations are:

Sometimes the last pushed stack element is made accessible for immutable access (for read) or mutable access (for write):

Stacks allow a very simple hardware implementation. They are common in almost all processors. In programming, stacks are also very popular for their way (LIFO) of resource management, usually memory. Nested scopes of language objects are naturally implemented by a stack (sometimes by multiple stacks). This is a classical way to implement local variables of a re-entrant or recursive subprogram. Stacks are also used to describe a formal computational framework. See stack machine. Many algorithms in pattern matching, compiler construction (e.g. recursive descent parsers), and machine learning (e.g. based on tree traversal) have a natural representation in terms of stacks.

Create a stack supporting the basic operations: push, pop, empty.

Let's start with the solution:

limit = 1000
dim stack(limit)

top = 0

sub push(n)
    if top < limit then
        top = top + 1 : stack(top) = n
    else
        print "stack full - ";
    end if
end sub

sub pop()
    if top then
        top = top - 1 : return stack(top + 1)
    else
        print "stack empty - ";
    end if
end sub

sub empty()
    return not top
end sub

// ======== test ========

for n = 3 to 5
    print "Push ", n : push(n)
next

print "Pop ", pop()

print "Push ", 6 : push(6)

while(not empty())
    print "Pop ", pop()
wend

print "Pop ", pop()