Data Structures, Algorithms, & Applications in C++
Chapter 8, Exercise 7

(a)

The extensions are

input( ):

Input a stack from bottom to top;

toString( ):

Return the stack elements, as a string, from bottom to top;

split(a, b):

Split a stack into the stacks a and b. Stack a contains the bottom-half elements, and stack b contains the remaining elements.

combine(a, b):

Combine the stacks a and b into a single stack. The elements in the combined stack are the result of placing stack b on top of stack a.