Question

这个小应用程序可以告诉驾驶员驱动程序运行的速度，当我测试该代码时，它只会警告第一个条件，无论我输入的内容是什么，而且这是一个严重的错误，这是我感谢所有帮助的代码提前给所有人

    alert(
        "Welcome this program tells you how fast you were driving your 
         vehicle, in km/h");

var top_speed = parseInt(prompt("How many km/h you was at?"));

if (top_speed >= 60) {
    alert("You were driving at " + top_speed + "km/h thats a normal speed");

} else if (top_speed >= 80) {
    alert("You were driving at " + top_speed + "km/h thats a moderate 
    speed");

} else if (top_speed >= 120) {
    alert("You were driving at " + top_speed + "km/h that is a very high 
    speed");

} else {
    alert("You need to go faster " + top_speed + "km/h is too slow ");
}

Answer 1

语句从上到下进行评估。由于80和120均为>= 60，因此第一个条件将始终与60或更高的值匹配。

只需切换顺序：

if (top_speed >= 120) {
    alert("You were driving at " + top_speed + "km/h that is a very high 
    speed");

} else if (top_speed >= 80) {
    alert("You were driving at " + top_speed + "km/h thats a moderate 
    speed");

} else if (top_speed >= 60) {
    alert("You were driving at " + top_speed + "km/h thats a normal speed");

} else {
    alert("You need to go faster " + top_speed + "km/h is too slow ");
}

一种替代方法是根据您的情况进行更具体的说明，即也包括一个上限：

if (top_speed >= 60 && top_speed < 80) {
    alert("You were driving at " + top_speed + "km/h thats a normal speed");

} else if (top_speed >= 80 && top_speed < 120) {
    alert("You were driving at " + top_speed + "km/h thats a moderate 
    speed");

} else if (top_speed >= 120) {
    alert("You were driving at " + top_speed + "km/h that is a very high 
    speed");

} else {
    alert("You need to go faster " + top_speed + "km/h is too slow ");
}

Answer 2

这是因为只要其他两个条件top_speed >= 60和true都为真，则第一个条件top_speed >= 80为top_speed >= 120。只要任何一个条件为true它不会检查低于此值的其他内容。您应该更改顺序。

var top_speed = parseInt(prompt("How many km/h you was at?"));

if (top_speed >= 120) {
    alert("You were driving at " + top_speed + "km/h that is a very high speed");

}
else if (top_speed >= 80) {
    alert("You were driving at " + top_speed + "km/h thats a moderate speed");
}  
else if (top_speed >= 60) {
    alert("You were driving at " + top_speed + "km/h thats a normal speed");

} 
 else {
    alert("You need to go faster " + top_speed + "km/h is too slow ");
}

Answer 3

您需要撤销检查条件：

试想一下，当您输入140时，该值大于60，因此代码将在第一个if条件下输入，而不会检查其他任何条件。

alert("Welcome this program tells you how fast you were driving your vehicle, in km/h");

var top_speed = parseInt(prompt("How many km/h you was at?"));

if (top_speed >= 120)
{
    alert("You were driving at " + top_speed + "km/h thats a very high speed");
}
else if (top_speed >= 80)
{
    alert("You were driving at " + top_speed + "km/h thats a moderate speed");
}
else if (top_speed >= 60)
{
    alert("You were driving at " + top_speed + "km/h that is a normal speed");
}
else
{
    alert("You need to go faster " + top_speed + "km/h is too slow ");
}

Answer 4

除了这里已经有好的答案（它们是正确的答案）之外，我认为在其他人遇到类似问题的情况下，我也应该提及这一点。

否则，仅当第一个条件为false时才执行。也就是说，一串其他ifs只会执行FIRST true条件。如果不存在，则仅执行else；否则，则不执行任何操作。

我的某些情况被忽略了

4 个答案: