Combinations & Permutations Calculator

by Daniel Echeverria

HTML

<p><strong>Calculate: </strong>
  Permutations <input type="radio" onclick="calc();" id="p" checked="checked" value="Permutations" name="type" onclick="P(n.value,r.value)">
  Combinations <input type="radio" onclick="calc();" id="c" value="Combinations" name="type" onclick="C(n.value,r.value)">
</p>
<p>
  <input type="text" id="r" onkeyup="calc();" />
  Objects<br />
From a Set of 
<br />
<input type="text" id="n" onkeyup="calc();"/>
Objects</p>

<div id="answer"></div>

JavaScript

function f(x) { 
		x == parseInt(x, 10);
		if(x==0) { 
			return 1; 
		} 
		return x * f(x-1); 
	}
	function P(n,r){
		return "<strong>Permutations:</strong> " + ( (f(n))/(f(n-r)) );
	}
	function C(n,r){
		return "<strong>Combinations:</strong> " + ( (f(n))/((f(n-r))*(f(r))) );
	}
	function calc(){
		y = document.getElementById('p').checked.valueOf();
		z = document.getElementById('c').checked.valueOf();
		n = document.getElementById('n').value;
		r = document.getElementById('r').value;
		if(y==true){ ans = P(n,r) };
		if(z==true){ ans = C(n,r) };
		document.getElementById('answer').innerHTML= ans;
	}