Question

Consider the function void change ( int \(* p\) ) \\{\\[ * p=20\\]\\} Show how to call the change function so that it sets the integer variable int i: to 20

Short answer

Answer: The purpose of using pointers when calling the 'change' function in this C++ example is to pass the memory address of the integer variable 'i' to the function. This allows the function to directly modify the value of 'i', instead of working with a copy of its value. By doing so, the changes made to 'i' inside the function are reflected in the original variable in the main program.

Step-by-step solution

Declare the integer variable i

Declare the integer variable 'i' that will be modified using the 'change' function: ```cpp int i; ```

Pass the memory address of i to the function

Use the '&' operator (address-of operator) to get the memory address of 'i', and pass it to the 'change' function as an argument. The function will modify the value of 'i' indirectly. ```cpp change(&i); ```

Complete Example

Here is the complete example including the 'change' function, declaration of the integer variable 'i', and calling the function with the address of 'i': ```cpp #include void change(int *p) { *p = 20; } int main() { int i; change(&i); std::cout << "The value of i is: " << i << std::endl; return 0; } ``` When this program is executed, it will modify the value of the integer variable 'i' to 20 using the 'change' function, and then print the result.

Key concepts

Memory Address

In C++, the concept of a "memory address" is integral to understanding how variables and pointers work. A memory address is a specific location in the computer's memory where a variable is stored. When you declare a variable, like ```cpp int i; ``` the operating system allocates a block of memory for this variable, and the address of this block is what we refer to as the memory address of the variable.

Knowing memory addresses allows you to work with pointers, which are variables that store these addresses rather than the actual data itself. For instance, in the exercise, the '&' operator is used to get the memory address of ```cpp i ```. Thus, ```cpp &i ``` represents the location in memory where 'i' is stored. This is crucial for giving functions access to variables outside their own scope.

• Memory addresses are essential for dynamic memory allocation.
• Pointers enable efficient handling of arrays and structures.
• Direct memory access helps in performance optimization.

Pass by Reference

The concept of "Pass by Reference" is at play when you pass pointers to functions. Unlike "Pass by Value," where you copy the actual data, "Pass by Reference" allows functions to modify the original variable by passing its address.

In the given C++ function, `change` modifies the variable `i` using its memory address. Here's how it works: when you call ```cpp change(&i); ``` you're passing the address of `i` to the function. Inside the function, the pointer ```cpp *p ``` directly accesses and changes the value stored at that address. Therefore, the original variable `i` is modified, and its value becomes 20.

• "Pass by Reference" is useful for memory efficiency, as it avoids copying large amounts of data.
• It allows functions to act on multiple outputs by altering referenced arguments.
• This mechanism is especially valuable for complex data structures.

Function Pointers

"Function Pointers" are a more advanced use of pointers in C++. They allow you to store the address of functions and call them indirectly through these stored addresses.

In scenarios like the one given, function pointers could allow you to dynamically choose which function to execute at runtime. Although they are not directly used in the described exercise, understanding them builds a strong foundation for dynamic function call mechanisms in your code.

• They enable callback functions in event-driven programs.
• Useful for implementing polymorphic behavior when templates or inheritance are overkill.
• Can lead to more flexible and reusable code structures.

Function pointers provide greater control over which functions execute, offering adaptability and enhancing program capabilities. They can be particularly powerful in systems requiring real-time function switch-out, such as state machines or GUI handlers.