References

lvalue references vs rvalue references (overview)

• Classic T& is an **lvalue reference** — binds to named objects.
• C++11 **T&&** is an rvalue reference — used for move semantics and perfect forwarding (advanced/move lesson territory).
• For this topic, master T& and const T& first — they cover most everyday APIs.

const correctness patterns

• const T& for input; T& for in/out; return T by value for new results (NRVO/moves often make this cheap).
• Do not take T& if you only read — callers cannot pass temporaries or const objects.
• Overload pairs sometimes exist: T& f(); and const T& f() const; in classes.

#include <string>
using namespace std;

string shout(const string& s) { // input only
    return s + "!";
}

void appendBang(string& s) { // in/out
    s += "!";
}

References, arrays, and structs

• You can have a reference to an array element: int& cell = a[i];
• Reference members in a class must be bound in the constructor initializer list.
• A reference parameter to a struct lets you update fields without copying the whole struct.

struct Account {
    int balance;
};

void deposit(Account& a, int amount) {
    a.balance += amount;
}

Alias — change via reference

#include <iostream>
using namespace std;

int main() {
    int marks = 80;
    int& m = marks;
    m += 5;
    cout << marks << "\n"; // 85
    return 0;
}

Pass by reference — deposit

#include <iostream>
using namespace std;

void deposit(int& balance, int amount) {
    balance += amount;
}

int main() {
    int bal = 1000;
    deposit(bal, 250);
    cout << bal << "\n"; // 1250
    return 0;
}

swap with references

#include <iostream>
using namespace std;

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

int main() {
    int x = 3, y = 7;
    swap(x, y);
    cout << x << " " << y << "\n";
    return 0;
}

const string& — no copy greet

#include <iostream>
#include <string>
using namespace std;

int wordCount(const string& s) {
    int spaces = 0;
    for (char ch : s) if (ch == ' ') spaces++;
    return s.empty() ? 0 : spaces + 1;
}

int main() {
    cout << wordCount("Learn Tech Guru") << "\n";
    return 0;
}

Range-for with references

#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> v = {5, 10, 15};
    for (int& n : v) n += 1;
    for (const int& n : v) cout << n << " ";
    return 0;
}

Struct updated by reference

#include <iostream>
#include <string>
using namespace std;

struct Student {
    string name;
    int marks;
};

void addBonus(Student& s, int bonus) {
    s.marks += bonus;
}

int main() {
    Student st{"Asha", 90};
    addBonus(st, 5);
    cout << st.name << " " << st.marks << "\n";
    return 0;
}

Return reference to smaller of two

#include <iostream>
using namespace std;

int& minRef(int& a, int& b) {
    return (a < b) ? a : b;
}

int main() {
    int x = 8, y = 3;
    minRef(x, y) = 0; // sets the smaller one to 0
    cout << x << " " << y << "\n"; // 8 0
    return 0;
}