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<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title></head><body><input type="text" name="num1" id="num1" value=""><select name="choice" id="choice"><option value="+">+</option><option value="-">-</option><option value="*">*</option><option value="/">/</option><option value="%">%</option></select><input type="text" name="num2" id="num2"><input type="button" id="calc" value="计算"><p id="res"></p><script>document.getElementById('calc').onclick = function () {var num1 = document.getElementById('num1').valuevar num2 = document.getElementById('num2').valuevar choice = document.getElementById('choice').valuevar res = ''if (num1 == '' || isNaN(num1 * 1)) res += '第一个输入框必须为数字'if (num2 == '' || isNaN(num2 * 1)) res += '第二个输入框必须为数字'if ((choice == '/' || choice == '%') && num2 * 1 == 0) res += '第二个输入框不能为零'num1 = num1 * 1;num2 = num2 * 1;if (!res) {switch (choice) {case '+':res = num1 + num2breakcase '-':res = num1 - num2breakcase '*':res = num1 * num2breakcase '/':res = num1 / num2breakdefault:res = num1 % num2}}document.getElementById('res').innerText = res}</script></body></html>
