while-loop will execute when there is a 0 in the while condition?

Question

Let's see the example code:

 var limit = 3;
 while(limit--){
   console.log(limit);
   if(limit){
     console.log("limit is true");
   }else{
     console.log("limit is false")
   }
 }

and the output will be:

2
"limit is true"
1
"limit is true"
0
"limit is false"

There is a 0, which means false in the last time while condition. Why the last time loop will execute?

It will first check (`limit` is still 1) and then decrement it. — Federico klez Culloca, Mar 05 '18 at 11:56
Look at what side the `--` is of the var limit.. it's on the right, meaning it will decrements after the comparison. If you want before you need `--limit` instead. — Keith, Mar 05 '18 at 11:58
The Reason is Post-decrement decreases the value after the operation has performed — Sagar Pudi, Mar 05 '18 at 11:59

Suresh Atta · Answer 1 · 2018-03-05T11:58:00.877

8

limit-- It is a post decrement. So when the limit is at 1 it resolves to true inside while and then it is actually decrementing hence when you printing it is 0.

edited Mar 05 '18 at 11:58

answered Mar 05 '18 at 11:57

Suresh Atta

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score 3 · Answer 2 · answered Mar 05 '18 at 12:01

while(limit--)

equals

while(limit){
    limit = limit -1;
}

so the limit is from 3 to 1 in while expression, while in braces, limit is from 2 to 0, so 'limit is false' will be executed. if you expect 'limit is false' doesn't execute, you can replace limit-- with --limit

score 3 · Answer 3 · answered Mar 05 '18 at 12:12

As you are using post increment it will first check condition and then will perform decrement on that variable so here while(limit--) will be treated as while(limit).

DRY RUN:

var limit = 3;

first time:

while(limit--){     //check limit while limit = 3 returns true and then decrement by 1 
   console.log(limit);  //so now print limit as 2
   if(limit){  //check limit while limit = 2
     console.log("limit is true");  //so now print this one
   }else{
     console.log("limit is false")
   }
 }

second time:

while(limit--){     //check limit while limit = 2 returns true and then decrement by 1 
   console.log(limit);  //so now print limit as 1
   if(limit){     //check limit while limit = 1
     console.log("limit is true");  //so now print this one
   }else{
     console.log("limit is false")
   }
 }

third time:

while(limit--){     //check limit while limit = 1 returns true and then decrement by 1 
   console.log(limit);  //so now print limit as 0
   if(limit){     //check limit while limit = 0
     console.log("limit is true");  
   }else{
     console.log("limit is false")  //so now print this one
   }
 }

fourth time:

it will not go in while loop as now limit = 0

score 0 · Answer 4 · answered Mar 05 '18 at 11:57

0

In several languages, 0 value is considered as a false value.

Also limit-- makes the decrement after being evaluated by the while condition.

answered Mar 05 '18 at 11:57

ADreNaLiNe-DJ

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score 0 · Answer 5 · answered Mar 05 '18 at 12:11

Here is a good way to look at it. We're looking at a number and seeing if it's above 0 before if it is we're taking away 1 and then running through the loop again otherwise we're stopping there.

let three = 3, two = 2, one = 1, zero = 0;

console.log('3--: ' + (three-- > 0));
console.log('2--: ' + (two-- > 0));
console.log('1--: ' + (one-- > 0));
console.log('0--: ' + (zero-- > 0));

while-loop will execute when there is a 0 in the while condition?

5 Answers5

DRY RUN: