Question

Consider the following statements: stackType stack(50); int num; Suppose that the input is: 31 47 86 39 62 71 15 63 Show what is output by the following segment of code: cin >> num; while (cin) { if (!stack.isFullStack()) { if (num % 2 == 0 || num % 3 == 0) stack.push(num); else if (!stack.isEmptyStack()) { cout << stack.top() << " "; stack.pop(); } else stack.push(num + 3); } cin >> num; } cout << endl; cout << "Stack Elements: "; while (!stack.isEmptyStack()) { cout << " " << stack.top(); stack.pop(); } cout << endl;

Short answer

Outputs during loop: 34 62; Stack Elements: 63 15 39 86.

Step-by-step solution

Initialize the Stack and Input Values

We start with an empty stack of size 50 and a sequence of numbers: 31, 47, 86, 39, 62, 71, 15, 63. We need to process each number one by one using the following code segment.

First Number (31) Processing

The first number, 31, is read. It is not divisible by 2 or 3. The stack is empty, so 31 + 3 = 34 is pushed onto the stack.

Second Number (47) Processing

The next number, 47, is read. It is neither divisible by 2 nor 3. The stack is not empty, so the top of the stack (34) is output, and 34 is popped from the stack.

Third Number (86) Processing

The next number, 86, is divisible by 2, so it is pushed onto the stack.

Fourth Number (39) Processing

The number 39 is divisible by 3, so it is pushed onto the stack.

Fifth Number (62) Processing

The number 62 is divisible by 2, so it is pushed onto the stack.

Sixth Number (71) Processing

The number 71 is neither divisible by 2 nor 3, so the top of the stack (62) is output and then popped from the stack.

Seventh Number (15) Processing

The number 15 is divisible by 3, so it is pushed onto the stack.

Eighth Number (63) Processing

The final number, 63, is divisible by 3, so it is pushed onto the stack.

Output Remaining Stack Elements

The main loop ends, and now each remaining stack element is output in the order they are popped. Elements are popped and printed, resulting in the order: 63, 15, 39, 86.

Key concepts

Control Structures

In C++, control structures are essential building blocks that dictate the flow of the program. They include loops and conditionals, helping you manage how your program executes.
A frequent and straightforward control structure is the **while loop**. It repeatedly executes a block of code as long as its condition remains true. In the provided exercise, `while (cin)` ensures that processing continues until there is no more input to read. This is determined by the condition of the input stream `cin`. It keeps iterating through the numbers provided in the input.
Control structures can be nested. In the code segment, nested within the `while` loop, are several `if` statements that help make decisions based on the current number. Such structured flow helps organize complex logic into understandable segments, making the code easier to manage and read.

Conditional Statements

Conditional statements in C++ allow for decision-making in your code. They enable specific actions to be taken when certain conditions are met. In the exercise, these are represented through `if`, `else if`, and `else` statements, allowing the program to decide what to do with the current number.
- **If Statements**: Evaluate a condition and execute the following block only if the condition is true. - **Else If Statements**: Provide additional conditions if the initial `if` statement's condition is false, offering alternatives. - **Else Statements**: Execute a block of code if none of the preceding conditions are true.
In the code example, the conditional statement `if (num % 2 == 0 || num % 3 == 0)` checks if a number is divisible by 2 or 3, determining whether it should be pushed onto the stack. This decision-making process is crucial for managing how the input numbers are handled and stored.

Stack Data Structure

A stack is a linear data structure following the Last In First Out (LIFO) principle. This means that the last element added to the stack is the first one to be removed. In C++, stacks are commonly managed using dynamic arrays or linked lists, with operations defined for pushing (adding) and popping (removing) elements.
In the exercise, a stack is used to store certain numbers based on specific conditions. The operation `stack.push(num)` adds an element to the top of the stack, while `stack.pop()` removes the most recent element added.
With functions like `stack.isFullStack()` and `stack.isEmptyStack()`, the program can efficiently manage and check the state of the stack, ensuring no overflows or underflows occur. Understanding these operations is vital for effectively using stacks in C++ and implementing algorithms like depth-first search, undo mechanisms in applications, and more.

Input/Output in C++

Input and output (I/O) operations are integral to any program, allowing it to interact with users or other systems. In C++, the `cin` and `cout` streams are common means to read data from the standard input (like the keyboard) and write data to the standard output (like the console).
In the provided exercise, `cin >> num` reads a number from the input stream into the variable `num`. This continues as long as there is data to read, governed by the `while (cin)` loop. When data needs to be displayed, `cout << stack.top() << " "` outputs the stack's current top element. This output process is crucial for providing feedback or results to the user, making it an essential skill for any C++ programmer to master. Mastering I/O operations in C++ allows for effective data processing and user interaction, forming the backbone of many practical applications.