1、負數是沒有階乘
2、0的階乘是1
3、整數的階乘n!=n*(n-1)*(n-2)....3*2*1
代碼
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>
<body>
<a>求階乘：</a><br/>
<input type="test" id="inputId" value="" />
<button onclick="factorial()">階乘</button>
<input type="test" id="resultId" value="" />
<script type="text/javascript">
function factorial() {
var inputObj = document.getElementById('inputId');
var result = parseInt(inputObj.value);
if (result < parseInt(0)) {
var resultObj = document.getElementById('resultId');
resultObj.value = "負數沒有階乘";
} else if (result === parseInt(0)) {
var resultObj = document.getElementById('resultId');
resultObj.value = "0的階乘是1";
} else {
for (var i = result - 1; i > 1; i--) {
result *= i;
}
var resultObj = document.getElementById('resultId');
resultObj.value = result;
}
}
</script>
</body>
</html>
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