Question

Assume that the following code is correctly inserted into a program: int s = 0; for (i = 0; i < 5; i++) { s = 2 * s + i; cout << s << " "; } cout << endl; a. What is the final value of s? (i) 11 (ii) 4 (iii) 26 (iv) none of these b. If a semicolon is inserted after the right parenthesis in the for loop statement, what is the final value of \(s ?\) (i) 0 (ii) 1 (iii) 2 (iv) 5 (v) none of these c. If the 5 is replaced with a 0 in the for loop control expression, what is the final value of \(s ?\) (i) 0 (ii) 1 (iii) 2 (iv) none of these

Short answer

a. (iii) 26; b. (i) 0; c. (i) 0.

Step-by-step solution

Analyzing Part (a)

The loop executes 5 times with the initial value of `s` being 0. We update `s` with the expression `2 * s + i` each time, then print `s`. - **Iteration 1 (i=0):** `s = 2 * 0 + 0 = 0` - **Iteration 2 (i=1):** `s = 2 * 0 + 1 = 1` - **Iteration 3 (i=2):** `s = 2 * 1 + 2 = 4` - **Iteration 4 (i=3):** `s = 2 * 4 + 3 = 11` - **Iteration 5 (i=4):** `s = 2 * 11 + 4 = 26` After the loop ends, the final value of `s` is 26.

Analyzing Part (b)

If a semicolon is inserted immediately after the for loop's parentheses, it creates an empty loop, neglecting the block meant to execute. The variable `s` remains unchanged throughout the loop iterations and retains its initial value, which is 0.

Analyzing Part (c)

Replacing `5` with `0` in the for loop control expression results in `i < 0` being evaluated before the loop starts, which is false initially. Thus, the loop body is never executed, and the value of `s` remains its initial value, `0`.

Key concepts

Loop Control Statements

In C++, loop control statements are essential for repeating a set of instructions until a specific condition is met. One of the most commonly used loops is the **`for` loop**. The `for` loop allows you to execute a statement or a block of statements multiple times. It consists of three main parts inside its parentheses: the initialization, the condition, and the increment/decrement expression.

• **Initialization:** Here, you initialize your loop control variable. For example, `int i = 0` sets up the loop to start counting from zero.
• **Condition:** This is a logical expression that is checked before each iteration. The loop continues as long as this condition evaluates to true.
• **Increment/Decrement:** This part updates the loop variable, bringing it closer to meeting the termination condition. For instance, `i++` increases `i` by 1 with each loop iteration.

The loop control statements ensure efficient program flow and help avoid hardcoding repetitive tasks. Understanding how to construct and manipulate these statements is crucial for any C++ programmer.

C++ Program Analysis

Analyzing a C++ program involves understanding its flow and behavior. Considering our given exercise, **program analysis** includes:

• **Variable Initialization:** We start by setting `s = 0`, which ensures a known starting state. This is vital since uninitialized variables can lead to unpredictable behavior.
• **Loop Execution:** The loop runs for 5 iterations (`i = 0` to `4`). During each iteration, the statement `s = 2 * s + i` is executed, modifying `s` based on its previous value and the current loop counter `i`.
• **Outcome Prediction:** By evaluating the expression change in each iteration, you can predict the program's final state, such as here where `s` reached a value of 26 after five cycles.

Effective program analysis requires the ability to predict how changes to code, such as inserting a semicolon or altering a loop condition, affect the outcome, as observed in parts (b) and (c) of the given problem.

Control Structures in C++

Control structures are fundamental in directing the flow of a program. In C++, these include decision-making structures, loops, and branch statements that allow your program to make logical choices and iterate through code.

**For Loop:** Acts as a control structure that efficiently repeats code. It allows for precise control over loop execution, including starting and ending conditions as well as iteration steps.

Moreover, inserting a semicolon directly after the loop header creates an empty loop, effectively skipping any intended block of code. Such small changes can drastically alter a program’s functionality.

• **Conditional Execution:** Neglecting parts of a loop through incorrect syntax or logic can result in dealing with default or initial values, as seen when initial values of variables are not altered.
• **Preemptive Checks:** Adjustments like modifying loop conditions (`i < 0` instead of `i < 5`) serve as checks before execution, ensuring no undesired iterations, hence no unintended side effects.

By mastering control structures, one can manipulate the flow, making your code both efficient and maintainable.