输入n，计算2的n次幂

1.利用for循环javascript <script type="text/javascript"> var n = parseInt(prompt('输入n')); var num = 1; for(var i = 0; i < n; i ++){ num *= 2; //num = num * 2; } document.write("2的" + n + "次幂是" + " " + num)

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