Question

Write the definition of ptr, a constant pointer to an int.

Short answer

Answer: To define a constant pointer to an integer variable in C++, follow these steps: 1. Initialize an integer variable, e.g. `int num = 5;` 2. Define the constant pointer using the syntax `int * const ptr = #`, where 'ptr' is the constant pointer pointing to the memory location of 'num'. 3. Use the constant pointer in your code, where the address it points to cannot be changed.

Step-by-step solution

Initialize an integer variable

To define a constant pointer, we need a variable to hold an integer value first. Let us declare an int variable and assign an initial value. ```cpp int num = 5; ```

Define constant pointer to an int

Next, we need to create a constant pointer to our integer variable. The syntax for defining a constant pointer to an int in C++ is: ``` int * const ptrName = &variableName ```

Implement the constant pointer

Now we define a constant pointer named 'ptr' to 'num': ```cpp int * const ptr = # ``` The complete code snippet should look like this: ```cpp #include int main() { int num = 5; int * const ptr = # std::cout << "Value of num: " << *ptr << std::endl; std::cout << "Address of num: " << ptr << std::endl; return 0; } ``` In this code, we have defined a constant pointer 'ptr' that holds the address of the integer variable 'num'. The pointer 'ptr' will always point to the memory location of 'num' and its address cannot be changed.

Key concepts

Constant Pointer

A constant pointer in C++ is a pointer that cannot be reassigned to point to another memory location once it is initialized. This behavior is enforced using the syntax: `int * const ptrName = &variableName;`. Here, `ptrName` is the name of the constant pointer, and `variableName` is the integer variable whose address is being assigned to the pointer.

A constant pointer has the following characteristics:

• The memory address it stores cannot change after initialization.
• You can modify the value at the address it points to, but you cannot update the pointer to point to something new.

In the given exercise, `ptr` is a constant pointer to the integer variable `num`. Once initialized, `ptr` will always point to `num`, ensuring a fixed relationship between the two in terms of memory address.

Memory Address

In computing, a memory address is a reference indicating a specific location in the computer's memory. Think of it like an exact GPS location, but instead of providing navigation, it helps the pointer locate and access the stored data in the memory.

Every variable in C++ has a memory address which can be accessed using the address-of operator `&`. For example, when you declare `int num = 5;`, `num` is stored at a specific memory address. When you use `&num`, C++ provides the exact memory address where `num` is stored.

Pointers use these addresses to refer to the specific memory location of the data. When the pointer `ptr` is defined as `int * const ptr = #`, it means the pointer now holds the memory address of `num`, allowing you to access or manipulate `num` through the pointer.

C++ Variables

In C++, a variable is essentially a storage location with a specific type, used to hold data. When you create a variable, you reserve a space in the computer's memory and assign it a name so you can easily refer to it.

Variables in C++ can be of multiple types, such as `int`, `float`, `char`, etc., each specifying what kind of data it can store. For instance, in `int num = 5;`, `num` is an integer variable with a value of 5. This tells the computer to reserve memory space suitable for an integer and store the number 5 in it.

Variables can be accessed and manipulated using pointers, providing more dynamic control over the data. By using pointers like `ptr`, which holds the address of `num`, you can directly work with the memory location of `num`, demonstrating the powerful combination of variables and pointers in C++.