Question

. What is the output of the following C++ code? int count = 1; int y = 100; while (count < 100) { y = y - 1; count++; } cout << " y = " << y << " and count = " << count << endl;

Short answer

The output is `y = 1 and count = 100`.

Step-by-step solution

Initialize the Variables

The code initializes two integer variables, `count` with 1 and `y` with 100. This means `count` starts at 1, and `y` starts at 100.

Analyze the While Loop Condition

The loop condition is `while (count < 100)`. This means the loop will continue to execute as long as `count` is less than 100. Initially, `count` is 1, which satisfies the condition.

Determine the Commands Inside the Loop

Inside the loop, two operations occur: `y = y - 1;` and `count++;`. The statement `y = y - 1;` decreases the value of `y` by 1 for each iteration, and `count++;` increases `count` by 1 during each iteration.

Calculate Iterations

Since the loop runs while `count` is less than 100, it will continue for 99 iterations (from count = 1 to count = 99). Each iteration decreases `y` by 1 and increases `count` by 1.

Final Values After Loop Completion

After 99 iterations, `count` becomes 100 (since it starts at 1 and increments by 1 each time). The variable `y`, which starts at 100 and decreases by 1 each time, will have decreased by 99. Therefore, `y` becomes 1.

Output the Values

The statement `cout << " y = " << y << " and count = " << count << endl;` prints the values of `y` and `count` after the loop has completed. Therefore, the output will be `y = 1 and count = 100`.

Key concepts

while loop

The **while loop** in C++ is an entry-controlled loop that allows you to repeat a block of code as long as a specified condition is true.
This particular loop is quite handy when you don't know beforehand how many times you need to execute the code inside it.
Let's delve a bit deeper into how it works. - **Syntax**: `while (condition) { /* code block */ }`
The condition is evaluated before the code inside the loop runs. If the condition is true, the code block will execute.
Then, the condition is evaluated again. This process continues until the condition becomes false. - **Example Explained**:
In our exercise, the condition is `count < 100`.
This means the loop will continuously execute its block as long as `count` remains less than 100.
Initially, `count` is 1, which satisfies the loop condition. - **Execution Flow**:
With each iteration, first `y` decreases by 1 and then `count` is incremented by 1.
The loop executes precisely 99 times, changing both `y` and `count`. When the condition eventually evaluates to false, in this case when `count` equals 100, the loop stops repeating.
Understanding this flow is key to mastering loops in C++.

variables in C++

**Variables** are fundamental to any programming language, including C++, as they store data for manipulation and use throughout an application.
C++ provides various types of variables such as `int`, `char`, `float`, and `double`, each serving different needs based on the data they hold. - **Definition**: In our example, two integer variables are defined: `int count = 1;` and `int y = 100;`
These create storage locations in memory to retain values throughout the program. - **Initialization**:
When a variable is declared and assigned a value at once, it's called initialization.
Here, `count` was initialized to 1, and `y` was set to 100 right at the beginning, specifying the starting point for these values. - **Modification**:
Variables in C++ can be easily modified.
Inside the while loop, we observed two operations:
`y = y - 1;` directly changes `y` by decrementing it, and `count++;` increments `count` by 1.
These modifications are crucial to the logic and execution steps of the program. Understanding how to declare, initialize, and manipulate variables helps you manage data efficiently throughout any C++ application.

C++ output statements

To communicate with users efficiently, C++ provides **output statements**, primarily through the use of the `cout` object.
Outputs are essential for displaying information on the screen, providing updates or results to the user based on the executed code. - **Basic Usage**: The syntax `cout <<` is used to send output to the console.
Here, we use the insertion operator `<<` to direct what we want to display.
In the given exercise, the statement `cout << " y = " << y << " and count = " << count << endl;` outputs the final values of `y` and `count`. - **Format Components**:
Text enclosed in double quotes is printed as is, like " y = " and " and count = " in our example.
Variables `y` and `count` are placed between the insertion operators to fetch their respective current values. - **End of Line**:
The `endl` is used for inserting a newline character, making the console output clear and neat.
This ensures anything printed afterward appears on the next line. Mastering output statements in C++ allows you to present clear, organized results and facilitate user interaction with programs.