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In this section, we will delve into the details of function parameters and return types in C++. Understanding these concepts is crucial for writing modular and reusable code. We will cover:

Function Parameters
Return Types
Practical Examples
Exercises

Function Parameters

Function parameters are the variables that you pass to a function when you call it. These parameters allow you to pass data into your functions, making them more flexible and reusable.

Types of Parameters

Value Parameters: These are the most common type of parameters. When you pass a value parameter to a function, the function gets a copy of the value. Changes made to the parameter inside the function do not affect the original value.
Reference Parameters: These parameters allow the function to modify the original variable. You use the & symbol to denote a reference parameter.
Constant Parameters: These are reference parameters that cannot be modified by the function. They are useful when you want to pass large objects to a function without copying them, but you don't want the function to modify the object.

Syntax

void functionName(int valueParam, int &refParam, const int &constParam) {
    // Function body
}

Example

#include <iostream>
using namespace std;

void modifyValues(int valueParam, int &refParam, const int &constParam) {
    valueParam = 20; // This will not affect the original variable
    refParam = 30;   // This will modify the original variable
    // constParam = 40; // This will cause a compilation error
}

int main() {
    int a = 10;
    int b = 15;
    int c = 25;

    modifyValues(a, b, c);

    cout << "a: " << a << endl; // Output: a: 10
    cout << "b: " << b << endl; // Output: b: 30
    cout << "c: " << c << endl; // Output: c: 25

    return 0;
}

Return Types

The return type of a function specifies the type of value that the function will return to the caller. If a function does not return a value, its return type is void.

Common Return Types

Primitive Types: int, float, double, char, etc.
Pointer Types: int*, char*, etc.
Reference Types: int&, string&, etc.
User-Defined Types: Classes, structs, etc.

Syntax

returnType functionName(parameters) {
    // Function body
    return value;
}

Example

#include <iostream>
using namespace std;

int add(int a, int b) {
    return a + b;
}

int main() {
    int result = add(5, 3);
    cout << "Result: " << result << endl; // Output: Result: 8
    return 0;
}

Practical Examples

Example 1: Swapping Two Numbers Using Reference Parameters

#include <iostream>
using namespace std;

void swap(int &x, int &y) {
    int temp = x;
    x = y;
    y = temp;
}

int main() {
    int a = 5, b = 10;
    cout << "Before swap: a = " << a << ", b = " << b << endl;
    swap(a, b);
    cout << "After swap: a = " << a << ", b = " << b << endl;
    return 0;
}

Example 2: Calculating Factorial Using Recursion

#include <iostream>
using namespace std;

int factorial(int n) {
    if (n <= 1) return 1;
    return n * factorial(n - 1);
}

int main() {
    int number = 5;
    cout << "Factorial of " << number << " is " << factorial(number) << endl;
    return 0;
}

Exercises

Exercise 1: Maximum of Two Numbers

Write a function max that takes two integers as parameters and returns the maximum of the two.

#include <iostream>
using namespace std;

int max(int a, int b) {
    // Your code here
}

int main() {
    int x = 10, y = 20;
    cout << "Max: " << max(x, y) << endl; // Output: Max: 20
    return 0;
}

Solution:

#include <iostream>
using namespace std;

int max(int a, int b) {
    return (a > b) ? a : b;
}

int main() {
    int x = 10, y = 20;
    cout << "Max: " << max(x, y) << endl; // Output: Max: 20
    return 0;
}

Exercise 2: Sum of Array Elements

Write a function sumArray that takes an array and its size as parameters and returns the sum of its elements.

#include <iostream>
using namespace std;

int sumArray(int arr[], int size) {
    // Your code here
}

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int size = sizeof(arr) / sizeof(arr[0]);
    cout << "Sum: " << sumArray(arr, size) << endl; // Output: Sum: 15
    return 0;
}

Solution:

#include <iostream>
using namespace std;

int sumArray(int arr[], int size) {
    int sum = 0;
    for (int i = 0; i < size; i++) {
        sum += arr[i];
    }
    return sum;
}

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int size = sizeof(arr) / sizeof(arr[0]);
    cout << "Sum: " << sumArray(arr, size) << endl; // Output: Sum: 15
    return 0;
}

Conclusion

In this section, we explored function parameters and return types in C++. We learned about value, reference, and constant parameters, and how to use them effectively. We also covered different return types and provided practical examples to solidify your understanding. Finally, we included exercises to help you practice these concepts. In the next section, we will dive into function overloading, which allows you to define multiple functions with the same name but different parameters.

Function Parameters and Return Types