Question

Consider the following statements: stackType stack; int num1, num2; Show what is output by the following segment of code: stack.push(12); stack.push(5); num1 = stack.top() + 3; stack.push(num1 + 5); num2 = stack.top(); stack.push(num1 + num2); num2 = stack.top(); stack.pop(); stack.push(15); num1 = stack.top(); stack.pop(); while (!stack.isEmptyStack()) { cout << stack.top() << " "; stack.pop(); } cout << endl; cout << "num1 = " << num1 << endl; cout << "num2 = " << num2 << endl;

Short answer

The stack outputs: '13 5 12'. Final num1 = 15, num2 = 21.

Step-by-step solution

Initialize Stack and Variables

We start with an empty stack `stackType stack` and two integer variables `num1` and `num2`.

Push Values onto the Stack

We push the integer value 12 onto the stack. Afterward, we push another integer value 5 onto the stack. The stack now contains 5 at the top and 12 below it: [5, 12].

Calculate num1

Retrieve the top of the stack (5) and add 3 to it, assigning the result (8) to `num1`. The stack remains unchanged: [5, 12].

Push New Value onto the Stack

Push `num1 + 5` (8 + 5 = 13) onto the stack. The stack now looks like [13, 5, 12].

Update num2

Assign the top of the stack (13) to `num2`. The stack remains unchanged: [13, 5, 12].

Modify Stack with num1 and num2

Push the sum of `num1` and `num2` (8 + 13 = 21) onto the stack. The stack becomes [21, 13, 5, 12].

Update and Modify Stack

Assign the top of the stack (21) to `num2` and pop it. The stack now looks like [13, 5, 12]. Push 15 onto the stack, making it [15, 13, 5, 12].

Update num1

Assign the top of the stack (15) to `num1` and pop it. The stack now looks like [13, 5, 12].

Output Stack Values

Using a loop, print all the stack values from top to bottom, popping each time: first 13, then 5, and finally 12. The output will be '13 5 12'. The stack is now empty.

Output num1 and num2

Output the final values of `num1` and `num2`: 'num1 = 15', 'num2 = 21'.

Key concepts

stackType class

In C++, a `stackType` class is often used to represent a stack data structure. A stack is a collection of items that follows the Last In, First Out (LIFO) principle. This means that the last item added to the stack is the first one to be removed.

The `stackType` class in C++ is typically templated, allowing you to create stacks that hold any data type. For example, `stackType` is a stack holding integers. The basic operations you can perform are:

• *Push*: Add an element onto the stack.
• *Pop*: Remove the top element from the stack.
• *Top*: Access the top element without removing it.
• *isEmptyStack*: Check whether the stack is empty.

By using a specific class like `stackType`, you group these operations into a neat package, making your code more organized and easier to maintain. It abstracts away the complex details and provides a simple interface to work with stacks.

push and pop methods

In C++, the push and pop methods are crucial operations for managing a stack. These methods manipulate the stack's state by adding and removing elements.

The **push** method adds an element to the top of the stack. This operation increases the size of the stack by one. For example, if you have a stack with integers, and you perform `stack.push(12)`, the number 12 is added to the top of the stack.
The **pop** method, in contrast, removes the element at the top of the stack. Since the stack follows a Last In, First Out (LIFO) order, the most recently added element is removed first. It's essential to ensure that the stack is not empty before calling pop to avoid errors.
Using these methods lets you control the flow of elements, enabling you to use the stack in a wide range of scenarios, such as managing function calls, undo functionality in applications, or as part of complex algorithms.

top method

The top method in a stack is used to access the topmost element in the stack, without removing it. This ability to peek at the top element without altering the stack's contents is very valuable in programming.

When you call `stack.top()`, it returns the value at the top of the stack. For example, if your stack contains [5, 12] with 5 being the top, then `stack.top()` will return 5. The stack remains unchanged after this operation. This is particularly useful in scenarios where you need to check the latest element added or make decisions based on it without modifying the stack.
It is important to ensure that the stack is not empty before attempting to access the top element. Accessing the top of an empty stack can lead to runtime errors, which can be avoided by using safety checks like `isEmptyStack` before calling the top method.

C++ variables and output

Variables in C++ are fundamental components used to store data that a program can manipulate. In the given problem, `int num1` and `int num2` are integer variables used to store numbers resulting from various stack operations.

In addition to storing values, these variables can be manipulated through expressions. For instance, `num1 = stack.top() + 3;` will assign to `num1` the value of the top element of the stack plus three.
The `cout` statement in C++ is utilized for outputting data to the console. In this problem, we use `cout` to print the contents of the stack and the values of `num1` and `num2`. By looping through the stack with a while loop and outputting each top value followed by a pop, we effectively display the stack's elements in order.
Understanding how to manipulate variables and output their values is crucial for debugging and ensuring that your program behaves as intended. It's an essential aspect of programming that helps you keep track of what's happening under the hood.