?獲取到的變量是字符串類型的不能進行運算，需要轉換類型。下面是我的代碼僅供參考
?function?count(){
????var?num1?=?document.getElementById("txt1").value;
????var?num2?=?document.getElementById("txt2").value;
????var?opt?=?document.getElementById("select").value;
????switch(opt){
????????case?"+":
????????????result?=?parseFloat(num1)?+?parseFloat(num2);
????????????break;
????????case?"-":
????????????result?=?parseFloat(num1)?-?parseFloat(num2);
????????????break;
????????case?"*":
????????????result?=?parseFloat(num1)?*?parseFloat(num2);
????????????break;
????????default:
????????????result?=?parseFloat(num1)?/?parseFloat(num2);
????}
????document.getElementById("fruit").value?=?result;
???}