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

The output is: 10 20 5 20

Step-by-step solution

Initial Variable Assignment

The code starts by initializing two integer variables, `alpha` and `beta`, with the values 5 and 10, respectively. So initially, we have:\[ \text{alpha} = 5, \quad \text{beta} = 10 \]

Evaluating the Condition

The `if` statement checks whether `beta` is greater than or equal to 10. In our case, `beta` is 10, which satisfies the condition \( \beta \geq 10 \). Therefore, the block of code inside the `if` statement will be executed.

Executing the If Block

Inside the `if` block, a new local variable `alpha` is declared with the value 10. This `alpha` is different from the `alpha` outside the `if` block due to the local scope of the variable. Thus, inside the block:\[ \text{alpha (local)} = 10 \]The statement `beta = beta + alpha;` updates `beta`:\[ \text{beta} = 10 + 10 = 20 \]Then, `cout << alpha << ' ' << beta << endl;` outputs the values of the local `alpha` and `beta` as:\[ 10 \quad 20 \]

Executing Code Outside the If Block

After completing the `if` block, control moves outside where we have `cout << alpha << ' ' << beta << endl;`. Here, `alpha` refers to the original `alpha` variable assigned before the `if` statement, and `beta` refers to the updated value. Thus, the output is:\[ 5 \quad 20 \]

Key concepts

Variable Initialization

In C++, variable initialization plays a critical role in defining the starting values of variables. When you declare a variable, it is a good practice to initialize it immediately. This not only sets a default value but also avoids potential garbage values that could be there from previous computations stored in memory.
Consider the code snippet from the exercise:

• `int alpha = 5;` initializes `alpha` with 5.
• `int beta = 10;` initializes `beta` with 10.

Both variables have been initialized as integers, and each has a specific value assigned. This ensures that when they are used later, they have predetermined values, making the code predictable and reducing room for error.
Also, note that inside the `if` block, a new initialization of `alpha` is done: `int alpha = 10;`. This re-initializes `alpha`, but only within the block's scope.

Conditional Statements

Conditional statements are fundamental to controlling the flow of a program. They allow certain pieces of code to run only when specific conditions are met. In our example, the `if` statement checks:

• `if (beta >= 10)`

The condition `beta >= 10` evaluates whether `beta` is greater than or equal to 10. If it is true, the program executes the code within the `{}` brackets.
In this case, the condition is true because `beta` is initialized to 10, so the code inside the `if` block gets executed.
This highlights the importance of using conditional statements for decision-making based on dynamic variables. They are the foundation of creating responsive and adaptable programs that can react to different inputs and states.

Local vs Global Scope

Understanding the difference between local and global scope is key in C++ programming. It delineates how variables are accessed and modified in different parts of a program.
In the given exercise, notice that there are two different `alpha` variables:

• The first `alpha` is global to the main function block, initialized as 5. This variable is accessible anywhere within this outer block.
• The second `alpha` is local to the `if` block, initialized as 10. This local variable `alpha` shadows the outer `alpha`, meaning within the `if` block, the new value of 10 is used.

Once the execution leaves the `if` block, the local `alpha` disappears, and the outer `alpha` comes back into play. This is pivotal because it prevents outer code from unintentionally altering values set within a specific local context and vice versa.
So, in the execution of `cout` after the `if` block, `alpha` regains its original initialized value of 5.