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C++ - FUNCTION

A Function in C++ is a chunk of Code that is used to conduct a particular task. And that chunk is only executed when it is called.

Say if you want to add two numbers, you can have an add Function that would be dedicated to add the numbers.

Similarly, if you want to divide two numbers, you can have a divide Function that would divide the numbers.

So, instead of placing all the codes in a single place. You can distribute the work among different Functions. So, that your code looks more structured and clean.

How a Function in C++ is created?

Below are the rules to create a Function :

A C++ function can be of any name(i.e. functionName mentioned above), followed by parentheses,i.e. (i.e. myFunction()).

Inside the parentheses, you can specify any number of parameters (i.e. myFunction(int x, int y)).

The block of code of the function should be inside the curly braces, i.e. {}.

There is a return statement which is an optional statement and returns the calculated result to the caller(i.e. return <return_variable>).

There is also a return type, which specifies the datatype of the returned value(i.e. return_type ).

As said, a Function is a chunk of Code used to conduct a task. And the block of code should be inside starting brace { and an ending brace }.

Below is how an add function would look like:

Example :

int add(int firstNumber, int secondNumber) 
{
	int result;
	result = firstNumber + secondNumber;
	return result;
}

And thats how we define a Function.

But it was mentioned in the Function description that a Function only executes only when it is called.

So, how a Function is called?

Let us see in the below example.

Note : Let us omit the argument and return type for now.

Example :

#include <iostream>
using namespace std;

void myFunction() {
	cout << "This is my first function";	
}

int main() {

    myFunction();
    return 0;  
}

Output :

This is my first function

So, in the above code, there are two parts,

The Function definition.
```
void myFunction() {
	cout << "This is my first function";
}
```
void used in the above function definition tells us that no values needs to be returned.

And the Function, call, inside the main() Function.
```
myFunction();
```

So, in the above code we have defined a Function, myFunction(). You can give any name to the Function(In this case we have given the name myFunction()).

void myFunction()
{
	cout << "This is my first function";
}

And the work of the Function, myFunction() is, just to print This is my first function.

Now, just remember one thing, the above Function, myFunction() will never execute until it is called.

And thus we have called the Function, myFunction() from Main() function.

int main()
{
	myFunction();
	return 0;
}

And the Function, myFunction() is called,

void myFunction()
{
	cout << "This is my first function";
}

Adding two numbers using Function and returning the result

Now, let us look at another example of adding two numbers and returning the result using aFunction.

Example :

#include <iostream>
using namespace std;

//Add function starts here.
int add(int firstNumber, int secondNumber) 
{
    int result;
    result = firstNumber + secondNumber;
    return result;
}

int main() {

    int firstNum = 5;
    int secondNum = 8;
    int addedResult;

    addedResult = add(firstNum,secondNum);

    cout << "The added value is : " << addedResult;
    
    return 0;
}

Output :

The added value is : 13

Let us explain the above example with a practical scenario.

Say you are given a task of adding two numbers. And you would follow the below steps to achieve it :

You would ask the firstNumber and secondNumber from the person who has given you this task.

And the above C++ Function expects the same thing.
```
int add(int firstNumber, int secondNumber)
```
Here, firstNumber and secondNumber are the two numbers which a C++ Function expects just like you.

Note : firstNumber and secondNumber are called as arguments that we will be learning in a separate tutorial.

And add() is the name of the Function.

In addition to that, there is something called as the return type(i.e. Int). Which we will be explaining soon.

The next thing you would do is, add the numbers and give the added value to the caller.

Same thing is done by the Above Function.

It adds firstNumber and secondNumber and stores the added value in a variable called result.
```
result = firstNumber + secondNumber;
```
It then returns the result to the caller(We will see next, who is a caller).
```
return result;
```
And since the returned value result is of type int. We have specified int in the returned type.

So far, we have seen how a Function works. Now, let us see who is the caller?

When the program execution begins,

And we initialise the first variable firstNum with the value 5.

int firstNum = 5;

Then in the next line, we have initialised the second variable secondNum with the value 4.

int secondNum = 8;

Then we call the add(int firstNumber, int secondNumber) Function.

addedResult = add(firstNum,secondNum);

And C++ searches for a Function with two arguments.

When it finds the Function, it assigns the value of firstNum to firstNumber and secondNum to secondNumber. And expects a value in return.

And gets into the block of the int add(int firstNumber, int secondNumber) Function.

This is where the numbers are added,

result = firstNumber + secondNumber;

And the result is stored in a variable result.

And in the next line we return the added value(i.e. result).

return result;

And the returned value goes back to the line, where the Function was called.

addedResult = add(firstNum,secondNum);

And the variable value gets the added result(i.e. 9) from the variable result.

And in the next line the added value is printed as output.

cout << "The added value is : " << addedResult;

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