I am using Notepad++ to create a simple web page where a user types in two numbers into a text box, and then presses a button. When they press the button something comes up
Html is a string, not a value. You need to parse it in someway.
EDIT:
The problem seems to be grabbing the values, change it to getElementById and it works fine:
http://jsfiddle.net/fHtZU/10/
HTML
Assignment 10
js
function greaterNum(){
var value1;
var value2;
value1 = document.getElementById("First_num").value;
value2 = document.getElementById("last_num").value;
if (value1 > value2){
alert(value1 - value2);
document.body.style.background = "orange";
}
}