Question

Suppose that the input is 25361816 -1. What is the output of the following code? int num; int sum; cin \(>>\) num; sum \(=\) num; while (num \(!=-1)\) \\{ sum \(=\) sum \(+\) num; cin \(>>\) num; } cout \(<<\) "Sum \(="<<\) sum \(<<\) endl;

Short answer

Output: Sum = 25361816.

Step-by-step solution

Understand the Problem Statement

The code is designed to read integers until \(-1\) is encountered. It then computes the sum of all input numbers including the first one but excluding \(-1\).

Analyze Initial Conditions

Initially, \( ext{num}\) is assigned the value obtained from the first input (25361816), and \( ext{sum}\) is initialized to this same value.

Execute Loop Logic

The loop continues to read input and add the number to \( ext{sum}\) while the input is not \(-1\). In this case, the loop only reads one more input, which is \(-1\), and does not alter the sum.

Compute and Identify the Output

Since the only number read besides \(-1\) is the initial input, \( ext{sum}\) remains as 25361816. Therefore, the output printed is "Sum = 25361816".

Key concepts

Input and Output Operations

In C++ programming, input and output operations are fundamental for interacting with the user or external systems. These operations primarily involve reading data from and writing data to the console using the `cin` and `cout` objects, respectively. Here, we focus on understanding how these work.

• `cin` (common input) is used to receive input data from the user. For example, `cin >> num;` reads an integer value entered by the user and stores it in the variable `num`.
• `cout` (common output) is used to display output to the console. For instance, `cout << "Sum = " << sum << endl;` prints the value of `sum` to the console, preceded by the string "Sum = ". The `endl` manipulator adds a newline at the end of the output, moving the cursor to the next line.

Remember that any data typed by the user is initially read as a character stream, and `cin` processes these inputs into suitable data types like `int`, `float`, or `string` as specified by the target variable.

While Loop

The `while` loop is a control structure that allows repeated execution of a block of code as long as a specified condition remains true. It's useful for situations where the number of iterations is not known beforehand, and the process might depend on user input or other runtime conditions. In the example, the loop is set up as `while (num != -1)`, which means that the block inside the loop will execute as long as `num` is not equal to -1.

• The condition is checked before each iteration. If `num` equals -1, the loop terminates, and the program continues after the loop's body.
• Inside the loop, `sum = sum + num;` accumulates the sum of the input numbers. This operation only executes if `num` is not -1, ensuring `-1` is excluded from the sum.
• The line `cin >> num;` at the end of the loop accepts a new integer from the user, potentially changing the loop condition.

The `while` loop is an efficient way to handle input streams until a particular condition is met, making it ideal for reading indeterminate data sequences.

Integer Variable Manipulation

Manipulating integer variables in C++ involves changing their values through arithmetic operations or assignments. In the provided exercise, understanding how integers are manipulated through assignments and additions is crucial. Each variable in C++ needs to be declared with a specific type, like `int` for integers.

• `int num;` declares a variable `num` that can hold integer values. Similarly, `int sum;` declares another integer variable `sum`.
• The assignment `sum = num;` initializes `sum` with the value of `num`. This is fundamental, as `sum` begins accumulating other values from here.
• Within the `while` loop, `sum = sum + num;` updates `sum` by adding the current value of `num`. This action represents cumulative addition, which is a key example of integer manipulation in loops.

These operations illustrate how integers can be manipulated to perform calculations in a program, forming the basis for more complex algorithms. Remember, when dealing with such operations, keeping an eye on data types (like ensuring you use integer operations for integer values) is essential.