Question

Suppose a program uses a stack of characters to read in a word and then write the word out backward as described in this section. Now suppose the input word is DAHL. List all the activations of the push and pop meth- ods. List them in the order in which they will be executed, and indicate the character that is pushed or popped. What is the output?

Answer 1

When the word 'DAHL' is entered, the program will use a stack to read the word in reverse. The program will push the characters 'D', 'A', 'H', and 'L' onto the stack and then pop them in reverse order, resulting in the output 'LHAD'.

Step-by-step explanation:

When the word 'DAHL' is entered, the program will use a stack to read the word in reverse. The stack data structure follows the Last-In-First-Out (LIFO) principle, which means that the character that is pushed last will be popped first.

1. The first character 'D' will be pushed onto the stack.
2. The second character 'A' will be pushed onto the stack.
3. The third character 'H' will be pushed onto the stack.
4. The fourth and final character 'L' will be pushed onto the stack.
5. The first character popped from the stack will be 'L'.
6. The second character popped from the stack will be 'H'.
7. The third character popped from the stack will be 'A'.
8. The fourth and final character popped from the stack will be 'D'.

Therefore, the output of the program when the input word 'DAHL' is entered will be 'LHAD'.