为什么我的比较没有产生预期的结果？

Question

I'm expecting this to output "Failed" but instead it outputs "Excellent", even though the value being compared doesn't match that comparison.

What's wrong with my code?

 let grade = 99; if(140 <= grade <= 150) { console.log('Excellent'); } else if(100 <= grade) { console.log('Very Good'); } else if(grade < 100) { console.log('Failed'); }

Answer 1

This is not how multiple comparisons are made:

if (140 <= grade <= 150)

In this case the first half would evaluate to true or false and the rest would be something like true <= 150 which makes little sense.

Instead, rather than think of it in terms of intuition, think of it in terms of combining logical operations. The two operations you want are:

• 140 <= grade
• grade <= 150

Combine those with the "and" operator:

if (140 <= grade && grade <= 150)

Result:

 let grade = 99; if (140 <= grade && grade <= 150) { console.log('Excellent'); } else if(100 <= grade) { console.log('Very Good'); } else if(grade < 100) { console.log('Failed'); }

Answer 2

If you meant to check whether the grade is between 140 and 150 by 140 <= grade <= 150 then you are doing it the wrong way. This will evaluate 140 <= grade first, which will return either zero or one, which will then be compared to 150 (and hence will always be smaller). You need to use two separate statements:

if(140 <= grade && grade <= 150) {
  ...
}

Answer 3

Do it like this. You need to separate two condition which you provided in the first if statement.

 let grade = 99; if(140<= grade && grade <=150){ console.log('Excellent'); } else if(100<= grade){ console.log('Very Good'); } else if(grade < 100){ console.log('Failed'); }

Answer 4

Expression 140 <= grade <= 150 is correct in mathematical form. In js you must write it as 140 <= grade && grade <=150