Is it possible to call another function:
========================================
function f1()
{
	body of statements
		for implementation
	f2()
}

function f2(){
	statements
		with implementation
	f1()
}

Calculator:
===========
Arithmetic
Logarithms
	log(a) + log(b)
	log(a+b)
Trigonometry
Integration
Differentiations


f1()
{
	addition
}
f2()
{
	log
	f1(a,b)
	log(result_f1)
}

// Calling a function inside another function

let sum = function(a,b,c,d,e)
{
    var result = a+b+c+d+e;
    return result;
}

var average = function(a,b,c,d,e)
{
    avg = sum(a,b,c,d,e) / 5;
    console.log("The Average = "+avg);   
}

var s = sum(12,13,14,15,16);
console.log("The Sum = "+s);

average(12,13,14,15,16);
=======================================
Q: WAP to find the factorial of the number.
===========================================

// A PROGRAM TO FIND THE FACTORIAL OF THE NUMBER.

let factorial = function(n)
{
    var fact = 1;

    if(n == 0)
    {
        return fact;
    }
    else if(n > 0)
    {
        num = n;
        while(num > 0)
        {
            fact = fact * num; // 7 42 210 
            num--; // 6 5
        }   
        return fact;
    }
    else
    {
        return "Factorial is not possible";
    }
}

console.log("The Factorial = "+factorial(-7));
==============================================
Recursion:
==========
==> Recursion Function
=======================
==> the function for the recursion,
	"recursion function"
==> Recursion
==============
	==> a process
	that can call the same function itself again and again until the completion of process.

let factorial = function(n)
{
    let fact = 1;
    if(n == 0)
    {
        return fact;
    }
    else if(n > 0)
    {
        return n * factorial(n-1); 
    }
    else{
        return "factorial is not possible.";
    }
}

console.log("The Factorial = "+factorial(6));


Syntax:
	function f1()
	{
		implementation;
		f1();
	}

===============================================
Pure Functions:
===============
1) Debugging is easy
2) Testing is easy.
3) Writing of Unit test cases easy.

let/var identifier = function(parameters)
{
	// can perform the action with only parameters.
		doesn't access the external values
	// cannot allow to modify the content of parameters 
}

=======================
// var a; 
let addition = function(a,b,c)
{
    // a = 100;
    // b = 200;
    // c = 300;

    return a+b+c;
}

console.log("The Sum = "+addition(10,20,30));