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Reference and Pointer

2025-12-15

Software Development with C and Cpp

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Reference vs Pointer#

Aspect	Reference	Pointer
Definition	An alias (another name) for an existing variable	A variable that stores the address of another variable
Initialization	Must be initialized when declared	Can be declared without initialization
Null value	Cannot be null	Can be null (`nullptr` / `NULL`)
Reassignment	Cannot be changed to refer to another object	Can point to a different object
Syntax usage	Used directly like a normal variable	Requires dereferencing (`*`) to access the value
Memory	Does not require separate memory	Requires its own memory to store an address
Safety	Safer, fewer chances of misuse	Less safe, can cause dangling or null pointer issues
Arithmetic	Not allowed	Pointer arithmetic is allowed
Use case	When you always refer to the same object	When you need optional references or dynamic allocation

Simple Example#

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int x = 10;
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int& ref = x;   // reference
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int* ptr = &x;  // pointer
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ref = 20;       // x becomes 20
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*ptr = 30;      // x becomes 30

One-Line Summary (Exam-Friendly)#

A reference is a constant alias to a variable and cannot be null or reassigned.
A pointer stores a memory address, can be null, and can be reassigned.

When to Use a Reference Parameter#

1. To modify the original argument#

Changes inside the function affect the caller’s variable.

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void increment(int& x) {
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    x++;
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}

📌 Use a reference when the parameter must exist and must not be null.

2. To avoid copying large objects#

More efficient than pass-by-value.

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void print(const string& s) {
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    cout << s;
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}

📌 Use a const reference when you don’t want to modify the object.

3. When the object should not change identity#

The function should always refer to the same object.

When to Use a Pointer Parameter#

1. When the parameter can be optional (nullable)#

A pointer can be nullptr, a reference cannot.

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void print(int* p) {
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    if (p != nullptr)
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        cout << *p;
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}

2. When the function needs to work with arrays or dynamic memory#

Common in low-level code.

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

3. When you need to change what the pointer points to#

(e.g., allocate or redirect memory)

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void allocate(int*& p) {
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    p = new int(10);
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}

Reference vs Pointer (Decision Guide)#

Situation	Use Reference	Use Pointer
Must not be null	✅	❌
Optional parameter	❌	✅
Avoid copying	✅	✅
Modify original object	✅	✅
Change what is referenced	❌	✅
Safer & cleaner code	✅	❌

Short Exam Answer#

Use a reference when the parameter must always refer to a valid object and you want safer, cleaner syntax.
Use a pointer when the parameter can be null, optional, or needs to be reassigned.

Reference and Pointer

https://mizuki.anka2.top/posts/l5-cpp-week12-lecture/reference-and-pointer/

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