Question

Suppose that you have the following function definition: void sum(int x, int y, int& z) { z = x + y; } Consider the following declarations: int list1[10], list2[10], list3[10]; int a, b, c; Which of the following function calls is valid? a. sum(a, b, c); b. sum(list1[0], list2[0], a); c. sum(list1, list2, c); d. for (int i = 1; i <= 10; i++) sum(list1[i], list2[i], list3[i]);

Short answer

Options a and b are valid; c is invalid due to improper argument types, and d is invalid due to an array index out-of-bounds issue.

Step-by-step solution

Understand Function Parameters

The function `void sum(int x, int y, int& z)` takes two integers by value (`x` and `y`) and one integer by reference (`z`). The integer passed to the parameter `z` will be modified by the function to store the sum of `x` and `y`.

Analyze Option a

The function call `sum(a, b, c);` is checked. All three variables `a`, `b`, and `c` are of type `int`. The first two arguments are passed by value, and the third is passed by reference. This usage matches the function signature, so it is valid.

Analyze Option b

In the call `sum(list1[0], list2[0], a);`, `list1[0]` and `list2[0]` are integers from the arrays `list1` and `list2`, and `a` is an integer variable. The function matches the signature because `list1[0]` and `list2[0]` are passed by value and `a` is passed by reference. This is valid.

Analyze Option c

Consider the function call `sum(list1, list2, c);`. The arguments `list1` and `list2` are arrays. Arrays cannot be passed by value in C++ like a single integer variable, thus violating the function signature. This option is invalid.

Analyze Option d

Examine the loop: `for (int i = 1; i <= 10; i++) sum(list1[i], list2[i], list3[i]);`. Here, `list1[i]` and `list2[i]` are accessed as individual integers of arrays, and so is `list3[i]`. However, this loop attempts to access indices from `1` to `10`, which will produce an error on `list[i]` due to out-of-bounds access at `list1[10]`. The valid indices range from `0` to `9`. Thus, while the function signature is respected, the range causes an error making this option invalid.

Key concepts

Function Parameters

In C++, understanding function parameters is crucial as they define the data inputs a function can handle. When defining a function like `void sum(int x, int y, int& z)`, there are two types of parameters involved:

• Pass by Value: `x` and `y` are passed by value, meaning the function gets a copy of these arguments, leaving the original values unchanged outside the function.
• Pass by Reference: `z` is a reference parameter, indicated by the `&`. This allows the function to modify the actual variable provided, as `z` holds a reference to it.

Understanding these parameters ensures correct function implementations and calls, enabling desired manipulations of data without unintended side effects.

Array Indexing

Array indexing is a method to access elements within an array using an index, which represents the element's position. In C++, arrays are zero-indexed. For example, in `int list[10];`, valid indices range from `0` to `9`. Let's break this down:

• Each element in `list` can be accessed using its index, such as `list[0]` for the first element or `list[9]` for the last.
• When referencing an element in a function call like `sum(list1[0], list2[0], a)`, you're accessing specific values within the arrays.
• Accessing out-of-bound indices, such as `list[10]`, causes errors or undefined behavior since it attempts to access invalid memory locations.

Array indexing is a fundamental technique, ensuring controlled and accurate data handling in C++ programs.

Reference Variables

Reference variables in C++ allow functions to modify variables directly, rather than working with copies. When a function parameter is a reference variable, as demonstrated by `int& z` in `sum(int x, int y, int& z)`, it becomes inherently powerful for certain operations.

• A reference is an alias, not a separate memory location. Changes to `z` directly alter the linked variable outside the function.
• Reference parameters are crucial for operations where the function needs to output multiple results or efficiently manipulate large data structures.
• They reduce memory overhead since copying large structures can be avoided, making programs more efficient.

The use of reference variables must be careful to ensure the references are valid and not inadvertently causing unwanted data changes.

C++ Syntax Rules

C++ syntax rules are the guidelines for writing valid source code. These rules ensure programs are logical and understood by the compiler. Let's touch upon some fundamental rules and best practices:

• Function Declarations: Specify the return type (`void` for no return) and parameter types (with reference denoted by `&`).
• Array Declaration: Arrays such as `int list[10];` specify the type and the size in the square brackets.
• Control Structures: Loops and conditionals (e.g., `for` loops) must be properly structured. Example: `for (int i = 0; i < 10; i++) { }` for valid array bounds access.
• Correct Indexing: Consider bounds when working with arrays to avoid errors, utilizing indices from `0` with care for data integrity.

Adhering to syntax rules not only prevents errors but also maintains code readability and effectiveness.