<!-- Begin
function addChar(input, character) {
if(input.value == null || input.value == "0")
input.value = character
else
input.value += character
}
function cos(form) {
form.display.value = Math.cos(form.display.value);}
function sin(form) {
form.display.value = Math.sin(form.display.value);}
function tan(form) {
form.display.value = Math.tan(form.display.value);}
function sqrt(form) {
form.display.value = Math.sqrt(form.display.value);}
function ln(form) {
form.display.value = Math.log(form.display.value);}
function exp(form) {
form.display.value = Math.exp(form.display.value);}
function sqrt(form) {
form.display.value = Math.sqrt(form.display.value);}
function deleteChar(input) {
input.value = input.value.substring(0, input.value.length - 1)
}
function changeSign(input) {
if(input.value.substring(0, 1) == "-")
input.value = input.value.substring(1, input.value.length)
else
input.value = "-" + input.value
}
function compute(form)  {
form.display.value = eval(form.display.value)}
function square(form)  {
form.display.value = eval(form.display.value) *
eval(form.display.value)}
function checkNum(str)  {
for (var i = 0; i < str.length; i++) {
var ch = str.substring(i, i+1)
if (ch < "0" || ch > "9") {
if (ch != "/" && ch != "*" && ch != "+" && ch !=
"-" && ch != "."
&& ch != "(" && ch!= ")") {
alert("invalid entry!")
return false
         }
      }
   }
return true
}
// End -->