<!-- 
function calculate() {
var userinput = document.calculator.input.value;
document.calculator.input.value = eval(userinput);
}
function plus() {
document.calculator.input.value += '+';
}
function minus() {
document.calculator.input.value += '-';
}
function mult() {
document.calculator.input.value += '*';
}
function div() {
document.calculator.input.value += '/';
}
function decimal() {
document.calculator.input.value += '.';
}
function num(x) {
document.calculator.input.value += x;
}
function plus_or_minus() {
document.calculator.input.value *= -1;
}

//-->