Taschenrechner

<html>
<head>
<script>
var lastVal=0;
var LasOP=0;
var replace=false;
function AddNum(val) {
	var ele = document.getElementById("T");


	if ((val != ',')&(val != '-')){
		if (replace==true){
			ele.innerHTML='0';
			replace=false;
		}
		if (ele.innerHTML=='0')
			ele.innerHTML='';
		ele.innerHTML = ele.innerHTML+val;
	} else if(val==',') {
		if (replace==true){
			ele.innerHTML='0';
			replace=false;
		}
		if (ele.innerHTML.indexOf(",")==-1)
			ele.innerHTML = ele.innerHTML+val;
	} else {
		
		if (ele.innerHTML.indexOf("-")==0){
			ele.innerHTML = ele.innerHTML.substr(1, ele.innerHTML.length-1);
		} else {
			ele.innerHTML= '-'+ele.innerHTML;
		}
	}


}
function Clear(val) {
	var ele = document.getElementById("T");
	ele.innerHTML='0'
	if (val=='A'){
		LasOP='0'
		lastVal='0'
	}
}
function Calc(val){
	var ele = document.getElementById("T");
	if (LasOP=='0')
		lastVal=Number(ele.innerHTML);
	if (LasOP=='+')
		lastVal=lastVal+Number(ele.innerHTML);
	if (LasOP=='-')
		lastVal=lastVal-Number(ele.innerHTML);
	if (LasOP=='*')
		lastVal=lastVal*Number(ele.innerHTML);
	if (LasOP=='/')
		lastVal=lastVal/Number(ele.innerHTML);	
	LasOP=val;
	ele.innerHTML=String(lastVal);
	replace=true;
}
</script>
</head>
<body>
<textarea id="T" readonly=true>0</textarea><br>
<button onclick="AddNum('1')">1</button><button onclick="AddNum('2')">2</button><button onclick="AddNum('3')">3</button>  <button onclick="Calc('+')">+</button><br>
<button onclick="AddNum('4')">4</button><button onclick="AddNum('5')">5</button><button onclick="AddNum('6')">6</button>  <button onclick="Calc('-')">-</button><br>
<button onclick="AddNum('7')">7</button><button onclick="AddNum('8')">8</button><button onclick="AddNum('9')">9</button>  <button onclick="Calc('*')">*</button><br>
<button onclick="AddNum('.')">,</button><button onclick="AddNum('0')">0</button><button onclick="AddNum('-')">-</button>  <button onclick="Calc('/')">/</button><br>
<button onclick="Clear('E')">CE</button><button onclick="Calc('=')">=</button><button onclick="Clear('A')">C</button>
</body>
</html>