Question

Write a function whose prototype is void exchange (int \(* p, \text { int } \star q)\) that takes two pointers to integer variables and exchanges the values in those variables.

Short answer

Question: Write a function that takes two pointers to integers as input and exchanges the values in those variables. Answer: To write a function that takes two pointers to integers as input and exchanges the values, you can create a temporary integer variable to store the value of the first integer variable and then assign the value of the second integer variable to the first integer variable. Finally, assign the temporary variable's value to the second integer variable. The function would look like: ```c void exchange(int *p, int *q) { int temp = *p; *p = *q; *q = temp; } ``` To test the function, you can call the exchange function with two integer variables' addresses as arguments and print the values of the variables before and after exchanging them.

Step-by-step solution

Understanding the function prototype

The function prototype given is 'void exchange(int *p, int *q)'. This means that the function takes two pointers to integers as input and doesn't return any value (void return type). The function's main task is to exchange the values of the two integer variables that the pointers are pointing to.

Write the function

To write the function, first create a temporary integer variable to store the value of the first integer variable (*p). Then, assign the value of the second integer variable (*q) to the first integer variable (*p). Finally, assign the temporary variable's value to the second integer variable (*q). The function looks like this: void exchange(int *p, int *q) { int temp = *p; // Store the value of the first integer variable *p = *q; // Assign the value of the second integer variable to the first integer variable *q = temp; // Assign the temporary variable's value to the second integer variable }

Test the function

To test the function, create a main function that calls the exchange function with two integer variables' addresses as arguments. Then, print the values of the variables before and after exchanging them to see if the function works as expected. #include void exchange(int *p, int *q); int main() { int a = 10; int b = 20; printf("Before exchange:\na = %d, b = %d\n", a, b); // Output: a = 10, b = 20 exchange(&a, &b); // Call the exchange function with addresses of a and b printf("After exchange:\na = %d, b = %d\n", a, b); // Output: a = 20, b = 10 return 0; }

Key concepts

Function Prototypes

In C++, a function prototype provides a blueprint or a declaration of a function before its actual implementation. This is crucial because it tells the compiler about the function's name, its return type, and the types of its parameters. For instance, the prototype `void exchange(int *p, int *q)` specifies a function named `exchange` that takes two parameters, both of which are pointers to integers, and returns nothing (`void`).

• Function prototypes are crucial when defining functions that will be used before they are implemented. They are usually declared in header files.
• Prototypes help in ensuring that the function calls match their definition and prevent errors during compilation.

Without a prototype, if you attempt to call a function that has not yet been defined, the compiler might not recognize it, leading to errors. Additionally, with a prototype, the compiler can catch mismatches in the number or types of arguments at compile time, rather than at runtime, making your code less prone to bugs.

Value Exchange using Pointers

Exchanging values between two variables using pointers is a fundamental concept in programming, especially in languages like C and C++. This concept leverages the power of pointers to directly manipulate memory addresses, allowing for efficient value swapping. Here's how it works: - A pointer is a variable that holds the address of another variable. When we use pointers, we can directly access and modify the memory location of variables. - In the `exchange` function, pointers `*p` and `*q` point to the memory locations of the two integers we want to swap. The process of exchanging values is fairly straightforward: 1. Store the value pointed to by `*p` in a temporary variable. 2. Assign the value pointed to by `*q` to the location pointed to by `*p`. 3. Assign the value stored in the temporary variable to the location pointed to by `*q`. This swaps the values efficiently without needing additional variables, aside from a temporary one for storage.

Testing Functions

Testing is an essential part of writing any function. It ensures that your code works correctly and as expected. When testing a function like `exchange`, you can follow these steps to verify its functionality: - Start by setting some initial values to the variables you will pass to the function. For instance, in the main function, we initialize `int a = 10` and `int b = 20`. - Print these initial values to confirm their state before the function call. This helps in comparing and verifying the output later. - Call the `exchange` function by passing the addresses of these variables (using `&a` and `&b`) to allow the function to manipulate the actual variables instead of copies. - After the function call, print the values again to check if the swap was successful. If `a` now holds the value of `b` and vice versa, your function works correctly. Creating such tests not only confirms the code behaves as intended but also makes it easier to understand how the function changes variable values through pointer manipulation.