C++ Functions Pass By Reference

🔁 C++ Functions – Pass By Reference

Pass by reference allows a function to work on the original variable, not on a copy.
Any change made inside the function directly affects the caller’s variable.

🔹 1. Why Pass By Reference?

  • Avoid copying data (faster)

  • Modify original values

  • Useful for large objects (arrays, structures, classes)

🔹 2. Basic Syntax

void functionName(dataType &parameter) {
// modify parameter
}

🔹 3. Simple Example

void change(int &x) {
x = 50;
}int a = 10;
change(a);

cout << a; // Output: 50

🔹 4. Pass By Value vs Pass By Reference

Pass by Value

void update(int x) {
x = 100;
}

❌ Original value not changed

Pass by Reference

void update(int &x) {
x = 100;
}

✔ Original value changed

🔹 5. Swap Two Numbers (Classic Example)

void swap(int &a, int &b) {
int temp = a;
a = b;
b = temp;
}int x = 5, y = 10;
swap(x, y);

🔹 6. Pass By Reference with Arrays

void modify(int arr[], int size) {
for (int i = 0; i < size; i++) {
arr[i] *= 2;
}
}

➡ Arrays are implicitly passed by reference.

🔹 7. Pass By Reference with Structures

struct Student {
int marks;
};void update(Student &s) {
s.marks = 90;
}

🔹 8. const Reference (Read-Only Reference)

void show(const int &x) {
cout << x;
}

✔ Prevents modification
✔ Efficient for large objects

🔹 9. Pass By Reference vs Pointer

ReferencePointer
Cleaner syntaxMore flexible
Cannot be NULLCan be NULL
No dereferencingNeeds *
SaferError-prone

❌ Common Mistakes

void fun(int &x) {
// ok
}fun(10); // ❌ cannot pass literal

✔ Correct:

int a = 10;
fun(a);

📌 Summary

  • Pass by reference modifies original variable

  • Use & in function parameters

  • Faster and memory-efficient

  • Use const & when modification is not needed

  • Preferred over pointers in many cases

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