gistfile1.js

$(document).ready(function() {

    $("body").children().remove();
    $("body").append("<div id='calc'><input type='text' id='ans' value='' /></div>");
    var btnVals = ['+','=','0','C','-','1','2','3','*','4','5','6','/','7','8','9'];
    for (var i = 0, ii = btnVals.length; i < ii; i++){
        if (i % 4 === 0) {
           $("#calc").append("<br/>");
         }
        $('#calc').append("<input type='button' value='" + btnVals.pop(0) + "' onclick='addit(this.value);'/>");
    }
});

 var addit = function(n) {
        
        switch(n) {
            case "C":
                document.getElementById('ans').value = "";
                break;
            case "=":
                document.getElementById('ans').value = eval(document.getElementById('ans').value);
                break;
            default:
                document.getElementById('ans').value += n;
                break;
                
        }
    };