C++ References

🔗 C++ References

A reference in C++ is an alias (another name) for an existing variable.
It does not create a new variable, but refers to the same memory location.

1. Declaring a Reference

int x = 10;
int &ref = x;

  • ref is a reference to x

  • Both share the same memory

2. Reference Example

int x = 5;
int &r = x;r = 10;

cout << x; // Output: 10

➡ Changing r also changes x.

 3. Reference vs Normal Variable

int a = 5;
int b = a;b = 10;

cout << a; // 5

int a = 5;
int &b = a;b = 10;

cout << a; // 10

4. References in Function Parameters (Very Important)

Without Reference (Call by Value)

void change(int x) {
x = 20;
}

❌ Original value not changed.

With Reference (Call by Reference)

void change(int &x) {
x = 20;
}

✔ Original value is changed.

Example:

int a = 10;
change(a);
cout << a; // 20

5. Swap Two Numbers Using References

void swap(int &a, int &b) {
int temp = a;
a = b;
b = temp;
}

6. Reference Must Be Initialized

❌ Invalid:

int &r; // error

✔ Valid:

int x = 10;
int &r = x;

 7. Reference Cannot Be Reassigned

int a = 10, b = 20;
int &r = a;r = b; // copies value of b into a

➡ r still refers to a.

8. const Reference

int x = 10;
const int &r = x;// r = 20; ❌ not allowed

✔ Useful for read-only access
✔ Prevents accidental modification

9. References with Arrays

int arr[3] = {1, 2, 3};

for (int &x : arr) {
x *= 2;
}

 10. Reference vs Pointer

ReferencePointer
Cannot be NULLCan be NULL
No reassignmentCan change address
Cleaner syntaxMore flexible
Must be initializedOptional initialization

📌 Summary

  • Reference = alias of a variable

  • Must be initialized

  • Cannot be NULL or reassigned

  • Used heavily in functions and loops

  • Safer alternative to pointers in many cases

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