Question

What is the output of the following code fragment? (Note: alpha and beta are int variables.) alpha = 5; beta = 10; if (beta >= 10) { int alpha = 10; beta = beta + alpha; cout << alpha << ' ' << beta << endl; } cout << alpha << ' ' << beta << endl;

Short answer

Outputs: '10 20' and '5 20'

Step-by-step solution

Initialize Variables

The code begins by declaring the integer variables alpha and beta. It assigns the value 5 to alpha, and the value 10 to beta.

Evaluate the Conditional Statement

The if statement checks if beta is greater than or equal to 10. Since beta is 10, which meets the condition, the code inside the block will be executed.

Declare a New Variable Inside the Block

Inside the if block, a new local variable alpha is declared with the initial value 10. This local alpha is separate from the alpha declared outside the block.

Modify the Value of beta

Within the block, beta is updated by adding the new local alpha (which is 10) to its current value, resulting in beta becoming 20.

Output Within the if Block

The values of the local alpha (10) and the modified beta (20) are printed, resulting in the first output: '10 20'.

Output Outside the Block

Outside the if block, the originally declared alpha (5) and the modified beta (20) are printed, leading to the second output: '5 20'.

Key concepts

Variable Scope

In C++, variable scope refers to the accessibility of a variable within parts of the program. When we declare a variable, it is only accessible within the block in which it is defined. A block is usually defined by curly braces `{}`.
For instance, in the given code, `int alpha = 10;` declared inside the `if` block is different from the `alpha` declared outside. They are two separate variables, even though they have the same name.
Variables declared outside of blocks are accessible to all subsequent code blocks, unless they are shadowed by a variable with the same name within a block. This is exactly what happens in our case; the local declaration of `alpha` in the `if` block shadows the main `alpha`. Remember:

• Outer variable scope -- accessible everywhere unless shadowed.
• Local variable scope -- accessible only within the block.

Understanding scope helps avoid unintended overwriting of variables and ensures code behaves as expected.

Control Structures

Control structures are used to dictate the flow of execution of a program. They can take several forms such as loops and conditionals.
In the given example, the `if` statement is a type of conditional control structure that allows for branching logic. It checks a condition and then executes the block of code inside if the condition is true.
Here, we use the `if` statement to determine whether to run the enclosed commands by evaluating `beta >= 10`. Since `beta` is initialized to 10, the condition is met, and the block's code executes. Control structures like this are fundamental as they allow programs to react differently based on input or other factors.
Remember to close your control structures with appropriate braces `{}` to accurately define which code falls under their control.

Output Operations

Output operations in C++ involve displaying information to the console or a file. The most common function used for this purpose is `cout`, which stands for "console output."
In our code snippet, `cout` is used to print values of variables to the console. Specifically, `cout << alpha << ' ' << beta << endl;` is used to display the variables `alpha` and `beta`, separated by a space. The `<<` operator is overloaded in C++ to work with `cout` and allows chaining of multiple insertion operations.
The `endl` manipulator at the end of the line tells the program to insert a new line afterwards, making sure subsequent output appears on a new line. By understanding the output operations, you can design your program to effectively communicate with the user or any observers.

Conditional Statements

Conditional statements in C++ allow the program to make decisions based on conditions. The `if` statement is the simplest form, allowing us to run code only if a specific condition is met.
In this example, `if (beta >= 10)` is the conditional statement. It evaluates whether `beta` is greater than or equal to 10. If the condition is true, the program executes the block of code inside the `if`. Otherwise, it skips the block.
This allows the program to operate dynamically depending on different inputs or situations. Conditional statements are a key part of making programs adaptable and responsive.
Additionally, it's possible to extend the basic `if` with `else` or `else if` for more complex decision-making processes. However, our current example uses a simple `if` to illustrate the fundamental concept.