Mastering C++ Functions - A Comprehensive Guide with 18 Practical Examples

Welcome to our guide on C++ Functions! In this guide, Learn everything about C++ functions with our in-depth guide. Covers function syntax, types, call stack, and includes 18 practical examples with code and explanations. Suitable for C++ learners of all levels, from beginner to intermediate.

What is a Function in C++?

A function in C++ is a reusable, independent unit of code that serves a specific purpose, streamlining your programming workflow. Functions help you organize your code, make it more readable, and save time by allowing you to reuse code instead of writing it multiple times.

Why Do We Need Functions in C++?

There are several reasons why functions are indispensable in C++ programming, such as:

Code reusability: Write once, use many times.
Modularity: Break down complex problems into smaller, manageable parts.
Readability: Make your code easier to understand and maintain.
Testing: Easily test individual parts of your program.
Abstraction: Hide complex implementations behind simple interfaces.

Function Syntax

Let’s break down the anatomy of a C++ function:

return_type function_name(parameter1_type parameter1_name, parameter2_type parameter2_name, ...) {
    // Function body
    // Code to be executed
    return value; // Optional, depending on return_type
}

Function Declaration

When declaring a function, you must specify its name, the type of value it returns, and the parameters it accepts, which informs the compiler about the function’s signature. It’s also called a function prototype.

int add(int a, int b); // Function declaration

Function Definition

The function definition includes the actual code that the function will execute.

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

Function Call

To utilize a function, you must include a function call in your code, which triggers the execution of the function’s logic.

int result = add(5, 3); // Function call

Function Name

Choose a descriptive name for your function that explains what it does. Use camelCase or snake_case for consistency.

Function Header

The three primary components of a function header are the return type, the function’s identifier, and the parameters that are passed to it.

int add(int a, int b)

Function Body

Within the function body, you’ll find the code that implements the function’s logic, enabling it to perform its designated operation.

{
    return a + b;
}

Function Parameters

Parameters are variables that hold values passed to the function when it’s called.

Function Return Types

A function’s return type determines the type of value it will return when called. It can be any valid C++ data type, including void for functions that don’t return a value.

Two Types of Functions in C++

Built-in Functions: These are pre-defined functions in C++ libraries, like cout, cin, sqrt, etc.
User-defined Functions: These are functions created by programmers to perform specific tasks in their programs.

Function Call Stack

The function call stack is a crucial concept in understanding how functions work behind the scenes. It keeps track of:

Function calls
Function names
Arguments/inputs
Local variables
Return values
Which function called which function

Upon function invocation, a new frame is pushed onto the call stack, and when the function execution is complete, its frame is popped off the stack.

Practice Questions With C++ Functions Code Examples

Let’s dive into some practical examples to help you understand functions better. Remember, all these programs are also available in our GitHub repository for your reference.

1. Write a function to print the sum of 3 numbers

#include <iostream>
using namespace std;

// Function to print sum of 3 numbers
void printSum(int a, int b, int c) {
    int sum = a + b + c;
    cout << "Sum of " << a << ", " << b << ", and " << c << " is: " << sum << endl;
}

int main() {
    printSum(10, 20, 30);
    return 0;
}

Output:

Sum of 10, 20, and 30 is: 60

2. Write a function to return the sum of 3 numbers

#include <iostream>
using namespace std;

// Function to return sum of 3 numbers
int getSum(int a, int b, int c) {
    return a + b + c;
}

int main() {
    int result = getSum(5, 10, 15);
    cout << "Sum is: " << result << endl;
    return 0;
}

Output:

Sum is: 30

3. Find maximum of three numbers

#include <iostream>
using namespace std;

// Function to find maximum of three numbers
int findMax(int a, int b, int c) {
    int max = a;
    if (b > max) max = b;
    if (c > max) max = c;
    return max;
}

int main() {
    int result = findMax(10, 30, 20);
    cout << "Maximum number is: " << result << endl;
    return 0;
}

Output:

Maximum number is: 30

4. Counting from 1 to n

#include <iostream>
using namespace std;

// Function to count from 1 to n
void countToN(int n) {
    for (int i = 1; i <= n; i++) {
        cout << i << " ";
    }
    cout << endl;
}

int main() {
    countToN(5);
    return 0;
}

Output:

1 2 3 4 5

5. Check prime or not prime number

#include <iostream>
using namespace std;

// Function to check if a number is prime
bool isPrime(int n) {
    if (n <= 1) return false;
    for (int i = 2; i * i <= n; i++) {
        if (n % i == 0) return false;
    }
    return true;
}

int main() {
    int num = 17;
    if (isPrime(num)) {
        cout << num << " is prime." << endl;
    } else {
        cout << num << " is not prime." << endl;
    }
    return 0;
}

Output:

17 is prime.

6. Check number is even or odd

#include <iostream>
using namespace std;

// Function to check if a number is even or odd
string evenOrOdd(int n) {
    return (n % 2 == 0) ? "even" : "odd";
}

int main() {
    int num = 7;
    cout << num << " is " << evenOrOdd(num) << "." << endl;
    return 0;
}

Output:

7 is odd.

7. Sum of all numbers up to 1 to N

#include <iostream>
using namespace std;

// Function to calculate sum of numbers from 1 to N
int sumToN(int n) {
    return (n * (n + 1)) / 2;
}

int main() {
    int n = 10;
    cout << "Sum of numbers from 1 to " << n << " is: " << sumToN(n) << endl;
    return 0;
}

Output:

Sum of numbers from 1 to 10 is: 55

8. Sum of all even numbers up to 1 to n

#include <iostream>
using namespace std;

// Function to calculate sum of even numbers from 1 to N
int sumEvenToN(int n) {
    return n * (n + 1);
}

int main() {
    int n = 10;
    cout << "Sum of even numbers from 1 to " << n << " is: " << sumEvenToN(n) << endl;
    return 0;
}

Output:

Sum of even numbers from 1 to 10 is: 110

9. Function to find area of circle

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

// Function to calculate area of a circle
double circleArea(double radius) {
    return M_PI * radius * radius;
}

int main() {
    double radius = 5.0;
    cout << "Area of circle with radius " << radius << " is: " << circleArea(radius) << endl;
    return 0;
}

Output:

Area of circle with radius 5 is: 78.5398

10. Function to find factorial of a number

#include <iostream>
using namespace std;

// Function to calculate factorial of a number
long long factorial(int n) {
    if (n == 0 || n == 1) return 1;
    return n * factorial(n - 1);
}

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

Output:

Factorial of 5 is: 120

11. Print all prime numbers from 1 to N

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

// Function to check if a number is prime
bool isPrime(int n) {
    if (n <= 1) return false;
    for (int i = 2; i * i <= n; i++) {
        if (n % i == 0) return false;
    }
    return true;
}

// Function to print all prime numbers from 1 to N
void printPrimes(int n) {
    for (int i = 2; i <= n; i++) {
        if (isPrime(i)) {
            cout << i << " ";
        }
    }
    cout << endl;
}

int main() {
    int n = 20;
    cout << "Prime numbers from 1 to " << n << " are: ";
    printPrimes(n);
    return 0;
}

Output:

Prime numbers from 1 to 20 are: 2 3 5 7 11 13 17 19

12. Print all digits of an integer

#include <iostream>
using namespace std;

// Function to print all digits of an integer
void printDigits(int n) {
    if (n < 10) {
        cout << n << " ";
        return;
    }
    printDigits(n / 10);
    cout << n % 10 << " ";
}

int main() {
    int num = 12345;
    cout << "Digits of " << num << " are: ";
    printDigits(num);
    cout << endl;
    return 0;
}

Output:

Digits of 12345 are: 1 2 3 4 5

13. Creating a number using digits

#include <iostream>
using namespace std;

// Function to create a number from digits
int createNumber(int digits[], int n) {
    int num = 0;
    for (int i = 0; i < n; i++) {
        num = num * 10 + digits[i];
    }
    return num;
}

int main() {
    int digits[] = {1, 2, 3, 4, 5};
    int n = sizeof(digits) / sizeof(digits[0]);
    cout << "Number created from digits: " << createNumber(digits, n) << endl;
    return 0;
}

Output:

Number created from digits: 12345

14. Print binary representation of a decimal number

#include <iostream>
using namespace std;

// Function to print binary representation of a decimal number
void printBinary(int n) {
    if (n > 1) {
        printBinary(n / 2);
    }
    cout << n % 2;
}

int main() {
    int num = 10;
    cout << "Binary representation of " << num << " is: ";
    printBinary(num);
    cout << endl;
    return 0;
}

Output:

Binary representation of 10 is: 1010

15. Convert KM into Miles

#include <iostream>
using namespace std;

// Function to convert kilometers to miles
double kmToMiles(double km) {
    return km * 0.621371;
}

int main() {
    double km = 10.0;
    cout << km << " kilometers is equal to " << kmToMiles(km) << " miles." << endl;
    return 0;
}

Output:

10 kilometers is equal to 6.21371 miles.

16. Convert Fahrenheit to Celsius

#include <iostream>
using namespace std;

// Function to convert Fahrenheit to Celsius
double fahrenheitToCelsius(double fahrenheit) {
    return (fahrenheit - 32) * 5 / 9;
}

int main() {
    double fahrenheit = 98.6;
    cout << fahrenheit << " Fahrenheit is equal to " << fahrenheitToCelsius(fahrenheit) << " Celsius." << endl;
    return 0;
}

Output:

98.6 Fahrenheit is equal to 37 Celsius.

17. Count all set bits of a number

#include <iostream>
using namespace std;

// Function to count set bits in a number
int countSetBits(int n) {
    int count = 0;
    while (n) {
        count += n & 1;
        n >>= 1;
    }
    return count;
}

int main() {
    int num = 15;
    cout << "Number of set bits in " << num << " is: " << countSetBits(num) << endl;
    return 0;
}

Output:

Number of set bits in 15 is: 4

18. Check even/odd using bitwise operator

#include <iostream>
using namespace std;

// Function to check if a number is even or odd using bitwise operator
bool isEvenBitwise(int n) {
    return !(n & 1);
}

int main() {
    int num = 7;
    cout << num << " is " << (isEvenBitwise(num) ? "even" : "odd") << "." << endl;
    return 0;
}

Output:

7 is odd.

Conclusion

Functions are the building blocks of C++ programming. They help you write cleaner, more organized, and reusable code. By mastering functions, you’ll be able to tackle more complex programming challenges and create efficient solutions. Keep practicing with these examples and don’t hesitate to create your own functions for specific tasks. Remember, the key to becoming a great programmer is consistent practice and curiosity to learn more.

~~ Happy coding!