Built-in vs. User-defined Functions: A Comprehensive Guide

Functions:

–Doing specific task.

–They help in modularizing code,

–improving readability,

 -reusing logic across the program.

return_type function_name(parameters) {

    // Function body

    return value;

}

Types of Functions:

1. Built-in Functions: Predefined functions provided by the C++ standard library, such as cout, cin, sqrt, etc.
2. User-defined Functions: Functions written by the programmer to perform specific tasks.

#include <iostream>

using namespace std;

// User-defined function

int add(int a, int b) {

    return a + b;

}

int main() {

    int  a1= 20, b1 = 30;

    cout << “Sum: ” << add(a1, b1) << endl; // Call the function

    return 0;

}

Key Components of a Function

1. Function Declaration/Prototype: Specifies the function name, return type, and parameters. It’s optional to declare before definition if defined before use.

int add(int a, int b);

2. Function Definition: The actual implementation of the function.

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

3. Function Call: Invokes the function in the program.

add(num1, num2);

#include <iostream>
using namespace std;

// User-defined function
int add(int a, int b) {
return a + b;
}

int main() {
int num1 = 10, num2 = 20;
cout << “Sum: ” << add(num1, num2) << endl; // Call the function
return 0;
}

Types of User-defined Functions

1. Void Functions: Do not return any value.

void printMessage() {
cout << “Hello, World!” << endl;
}

2. Parameterized Functions: Accept parameters.

int multiply(int x, int y) {    return x * y;}

3. Function with Default Arguments:

int sum(int a, int b = 5) { // b has a default value of 5
return a + b;
}

4. Inline Functions: Defined with the inline keyword for small, frequently used functions.

inline int square(int x) {
return x * x;
}

5. Recursive Functions: A function that calls itself.

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

Passing Parameters

• Pass by Value: A copy of the variable is passed to the function.
• Pass by Reference: The actual variable is passed, and changes affect the original.

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

• Pass by Pointer: A pointer to the variable is passed.

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

Function Overloading:

Multiple functions can have the same name but different parameter lists.

#include <iostream>
using namespace std;

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

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

int main() {
cout << add(5, 10) << endl; // Calls int version
cout << add(5.5f, 10.5f) << endl; // Calls float version
return 0;
}

Advantages of Functions

1. Reusability of code.
2. Better organization and readability.
3. Easier debugging and testing.