在while循环中放错地方的Break语句答案

【问题标题】：Break statement misplaced in while-loop在while循环中放错地方的Break语句
【发布时间】：2017-03-31 08:30:04
【问题描述】：

我想创建一个脚本，从列表（数组）中询问您想要的项目，检查项目是否有库存，如果您输入“列表”，则显示库存并退出程序（while 循环）如果你输入“退出”

while (true) { // endless loop
  var search = prompt('Type the item you are looking for, type "list" to display the inventory, type "quit" to exit te store.');
  search = search.toLowerCase;
}
if (search = 'quit') {
  break; // if the client types quit, they exit the store, loop ends
} else if search == 'list'{
  write('<p>We currently have ' + inventory.join(', ') + ' in stock.</p>');
} else if (inventory.indexOf(search) > - 1) {
  write('<p>Yes, we have ' + search + ' in our stock.</p>');
} else {
  write('<p>Sorry, we don\'t have ' + search + ' in our stock</p>');
}

break 语句不在循环中，但我真的不知道它应该去哪里......

有什么想法吗？

【问题讨论】：

你的开发者工具控制台中的任何错误......沿着SyntaxError: unlabeled break must be inside loop or switch的行......哦，你不会......因为你的代码永远不会因为无休止的while循环而走到那一步
also ... = assignment ... == 和 === 相等性测试
整个if 放错了位置。
呃，你为什么不把整个事情放在循环中呢？你不想在再次循环之前对 prompt 结果做点什么吗？

标签： javascript syntax while-loop

【解决方案1】：

只需将整个“if”结构放在“while”循环中！

即，将“}”从第 4 行移到代码末尾。

“break”将与“while”构造相关。

【讨论】：

【解决方案2】：

您的代码中至少有三个错误：

首先 if 在循环之外。其次，您错过了一个 if 语句周围的括号。第一个 if 语句中的第三个你错过了第二个等号

var search='1';
while (true) { // endless loop
  var search = prompt('Type the item you are looking for, type "list" to display the inventory, type "quit" to exit te store.');
  search = search.toLowerCase;

if (search == 'quit') {
  break; // if the client types quit, they exit the store, loop ends
} else if (search == 'list'){
  write('<p>We currently have ' + inventory.join(', ') + ' in stock.</p>');
} else if (inventory.indexOf(search) > - 1) {
  write('<p>Yes, we have ' + search + ' in our stock.</p>');
} else {
  write('<p>Sorry, we don\'t have ' + search + ' in our stock</p>');
}
}

【讨论】：

【解决方案3】：

试试这个。您在 if 语句中放错了括号，也错过了 ==；

while (true) { // endless loop
  var search = prompt('Type the item you are looking for, type "list" to display the inventory, type "quit" to exit te store.');
  search = search.toLowerCase;

if (search == 'quit') {
  break; // if the client types quit, they exit the store, loop ends
} else if search == 'list'{
  write('<p>We currently have ' + inventory.join(', ') + ' in stock.</p>');
} else if (inventory.indexOf(search) > - 1) {
  write('<p>Yes, we have ' + search + ' in our stock.</p>');
} else {
  write('<p>Sorry, we don\'t have ' + search + ' in our stock</p>');
}
}

【讨论】：

【解决方案4】：

您的代码中有几个错误，有些是语法错误，例如缺少括号，或者只使用了一个等号。 break 关键字必须在循环内，否则将没有循环可以跳出。

但是，如果不是我们说if(!search) continue; 的部分，而是说if(!search) break;，您可以通过单击取消或输入一个空字符串来跳出循环，如果您问我这更有意义。

var inventory = ['tea','sugar'];
while (true) { // endless loop
  var search = prompt('Type the item you are looking for, type "list" to display the inventory, type "quit" to exit te store.');

  if(!search) continue;

  search = search.toLowerCase();

  if (search == 'quit') {
    break; // if the client types quit, they exit the store, loop ends
  } else if (search == 'list') {
    alert('<p>We currently have ' + inventory.join(', ') + ' in stock.</p>');
  } else if (inventory.indexOf(search) > -1) {
    alert('<p>Yes, we have ' + search + ' in our stock.</p>');
  } else {
    alert('<p>Sorry, we don\'t have ' + search + ' in our stock</p>');
  }
}

【讨论】：

【解决方案5】：

您应该在 while 循环中检查您的数据，并在需要时将其中断。

我还更正了错误并测试了脚本。

您可以在我的 cmets 中找到有关错误的详细信息。

while (true) { // endless loop
  var search = prompt('Type the item you are looking for, type "list" to display the inventory, type "quit" to exit te store.');
  search = search.toLowerCase();
      // After getting user input you want to check it and decide accordingly if
  // you want to stop the loop or you want to ask the user for input again
  if (search == 'quit') { // *** ERROR *** In your code you used a
// single = and that doesn't work for comparison in Javascript
    break; // if the client types quit, they exit the store, loop ends
  } else if (search == 'list') {// *** ERROR *** If you have more than a single if you need to always use parenthesis
    console.log('<p>We currently have ' + inventory.join(', ') + ' in stock.</p>');
  } else if (inventory.indexOf(search) > -1) {
    console.log('<p>Yes, we have ' + search + ' in our stock.</p>');
  } else {
    console.log('<p>Sorry, we don\'t have ' + search + ' in our stock</p>');
  }

}

【讨论】：