do-while loop is not behaving as expected

Question

I cannot figure out why this is returning 1 instead of 7.

 const getNextEventCountTest = () => {

        
        let sum = 0;
        let q = 0;

        do {
            sum = sum + 0.5
        }
        while (sum < 4){
         
            q = q + 1;
        }

        return q;
  };

do-while is good here, since I want to always run the first code block but only conditionally increment q.

But this:

console.log(getNextEventCountTest()); => 1

whereas this has the right behavior:

const getNextEventCountTest = () => {
  
        let sum = 0;
        let q = 0;

        // this is desired behavior:
        while (sum < 4){
            sum = sum + 0.5
            if(sum < 4){
               q = q + 1;
            }
        }

        return q;
  };

Perhaps because your code executes like do { ... } while(condition); { ... }. Notice the added semicolon — Peter Thoeny
– Peter Thoeny, Commented Nov 12, 2022 at 2:33
The language perils of optional semi-colons. It would be interesting to see what a good linter says about this code. — jfriend00
– jfriend00, Commented Nov 12, 2022 at 2:39
well it's been so long since I used a do-while lol, but the frankenstein construct I made up in OP has some value even though semantically it's a mess. Coincidentally intellij was forcing the braces after the while statement on a newline and I couldn't figure out why, now I know. — Alexander Mills
– Alexander Mills, Commented Nov 12, 2022 at 2:42

Peter Thoeny · Accepted Answer · 2022-11-12 02:37:31Z

2

This is because your code executes like do { ... } while(condition); { ... }. Notice the added semicolon - the second {} block executes once.

answered Nov 12, 2022 at 2:37

Peter Thoeny

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Comments

Saneesh · Accepted Answer · 2022-11-12 03:31:00Z

2

Your syntax is wrong regarding do while loop. Use this instead

do {
  //Your code that is to be executed
}
while(/* condition */);

I have improved the code for you;

const getNextEventCountTest = () => {
  let sum = 0, q = 0;

  // works only when sum and q are defined as an integer
  do{
     sum += 0.5
     if(sum < 4) q++;
  }
  while(sum < 4)
  return q;
}

Then, it will work as expected. Bye, have a great day!

edited Nov 12, 2022 at 3:31

answered Nov 12, 2022 at 3:17

Saneesh

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