🚩 Quick Explanation

1. Variables and Memory

   • A variable in C++ is just a box in memory that stores a value.

   int x = 10; // box named x stores 10
   

2. Pointers ( and &)

   • A pointer is a variable that stores the address of another variable.

   int x = 10;
   int* p = &x;   // p stores the address of x
   *p = 20;       // changes the value at that address → x becomes 20
   

   • &x = “address of x”
   • p = “value at the address p points to”

3. References (&)

   • A reference is just another name (alias) for a variable.

   int y = 5;
   int& ref = y; // ref is another name for y
   ref = 15;     // changes y to 15
   

   • References must be initialized when created and can’t be reseated.

⚖️ Key difference:

• Pointer can be reassigned to point elsewhere; reference is permanently tied to one variable.
• Pointer needs explicit dereferencing (p); reference acts like the variable itself.

📝 Practice Problems (in increasing difficulty)

1. Basics

   • Declare an integer a = 42.

   • Create a pointer p to a.

   • Print a, &a, p, and p.

     What’s the difference?

2. Modifying Values

   • Use the pointer p to change the value of a to 99.
   • Then create a reference r to a and change a to 123 using r.
   • Print a after each change.

3. Pointers and Functions

   • Write a function void square(int* n) that squares a number using a pointer.
   • Call it with a variable and confirm it changes.

4. References and Functions

   • Rewrite the above function as void square(int& n).
   • Compare the syntax and results.

5. Challenge

   • Write a function swap in two versions:

     a) Using pointers

     b) Using references

   • Test it with two integers and see both work.

Problem from Hackerrank:

Pointer | HackerRank