Passing by Value and Reference in a function.

·       Passing arguments to a function in two primary ways: pass by value and pass by reference.

 

1. Pass by Value

• Default Mechanism.
• When a parameter is passed by value, a copy of the argument’s value is made and passed to the function.
• The function works with this copy, and any modifications to it do not affect the original variable.

 

Syntax

void function_name(data_type parameter) {

    // Modify parameter

}

 

Example

#include <iostream>

using namespace std;

 

void increment(int x) {

    x++; // Modifies the copy, not the original

    cout << "Inside function: " << x << endl;

}

 

int main() {

    int num = 10;

    increment(num);

    cout << "Outside function: " << num << endl;

    return 0;

}

 

Output

Inside function: 11

Outside function: 10

 

Pros

• Safety: The original data is protected from modification.
• Simplicity: No unintended side effects.

 

Cons

• Memory Overhead: Copying large objects (e.g., structs, arrays) can be inefficient.
• No Direct Modification: You can’t change the original variable.

 

2. Pass by Reference

• Function receives a reference to the original variable (its memory address), not a copy.
• Changes made to the parameter inside the function directly affect the original variable.

 

Syntax

void function_name(data_type &parameter) {

    // Modify parameter (affects original)

}

 

Example

#include <iostream>

using namespace std;

 

void increment(int &x) {

    x++; // Modifies the original variable

    cout << "Inside function: " << x << endl;

}

 

int main() {

    int num = 10;

    increment(num);

    cout << "Outside function: " << num << endl;

    return 0;

}

 

Output

Inside function: 11

Outside function: 11

 

Pros

• Efficiency: No copying of data, especially useful for large objects like structs or classes.
• Direct Modification: Allows the function to alter the original variable.

 

Cons

• Risk: Unintended changes to the original data can occur.
• Clarity: You must be explicit about modifying behaviour to avoid confusion.

 

Pass by Pointer (Similar to Reference)

• Involves passing the memory address of a variable explicitly using pointers (*).
• Modify the original data via the pointer, but must dereference it manually.
• Requires explicitly passing the address (&num) and using dereference (*x).
• Allows handling nullptr safely.

 

Example:

#include <iostream>

using namespace std;

 

void increment(int *x) {

    (*x)++; // Dereference pointer to modify original

}

 

int main() {

    int num = 10;

    increment(&num); // Pass address of num

    cout << num << endl; // Outputs 11

    return 0;

}

 

Pointer vs. Reference

• Reference: Cleaner syntax, automatically dereferenced, cannot be null.
• Pointer: Explicit address manipulation, can be null, requires * to access the value.

 

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Key Differences

 

Feature	Pass by Value	Pass by Reference
Data Handling	Copy of the argument	Reference to the argument
Original data Modified	No	Yes
Syntax	type param	type &param
Memory Usage	Creates a copy (more memory)	No copy (less memory)
Use Case	Protect original data	Modify original data

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