Question

我无法弄清楚为什么这不起作用。如果我在提示符中输入“No”，则会再次给出相同的提示，这意味着再次执行do循环，因为while语句返回true。但是根据我的逻辑，当给出答案“否”时，while语句应返回false并结束do循环。当（answer！=“Yes”）为真且（answer！=“No”）为false时，“and”运算符不应返回false（true＆amp;＆amp; false ==假）？我在这里弄错了什么？其他一切都有效。

do {
  var answer = prompt("Do you want dinner? Yes or No."); 
} while (answer != "Yes" && "No");
if (answer == "Yes") {
  alert("Great, there is food in the fridge!"); }
else {
  alert("Ok. I will ask again later."); }

Answer 1

while条件错了。第二部分永远是真的。

试试这个：

while (answer != "Yes" && answer != "No");

Answer 2

function logAnswer(answer) {
  console.log(answer != "Yes" && "No");
}

logAnswer("Wub") --> false && true --> false
logAnswer("Yes") --> false && true --> false
logAnswer("No")  --> true && true  --> true

&& "No"将评估字符串＆＃34;否＆＃34;像真的一样。应该对answer进行两次评估。我个人认为OR操作符可能在这里读得更好。

while (!(answer == "Yes" || answer == "No"))  // OR operator
while (answer != "Yes" && answer != "No")    // AND operator

Answer 3

您的条件表格错误。

do {
  var answer = prompt("Do you want dinner? Yes or No."); 
} while (answer != "Yes" && answer != "No");
if (answer == "Yes") {
  alert("Great, there is food in the fridge!"); }
else {
  alert("Ok. I will ask again later."); }

Answer 4

您必须在&&的两边写一个完整的测试。 "No"将始终评估为true。

while (answer != "Yes" && answer != "No")

'和'似乎在'真假'时返回'true'（当回答== b，回答！= a＆amp;＆amp; b返回true）

4 个答案: