Test loops at the top or bottom? (while vs. do while) [closed]

When I was taking CS in college (mid 80's), one of the ideas that was constantly repeated was to always write loops which test at the top (while...) rather than at the bottom (do ... while) of the loop. These notions were often backed up with references to studies which showed that loops which tested at the top were statistically much more likely to be correct than their bottom-testing counterparts.

As a result, I almost always write loops which test at the top. I don't do it if it introduces extra complexity in the code, but that case seems rare. I notice that some programmers tend to almost exclusively write loops that test at the bottom. When I see constructs like:

if (condition)
{
    do
    {
       ...
    } while (same condition);
}

or the inverse (if inside the while), it makes me wonder if they actually wrote it that way or if they added the if statement when they realized the loop didn't handle the null case.

I've done some googling, but haven't been able to find any literature on this subject. How do you guys (and gals) write your loops?

Solution 1:

I always follow the rule that if it should run zero or more times, test at the beginning, if it must run once or more, test at the end. I do not see any logical reason to use the code you listed in your example. It only adds complexity.

Solution 2:

Use while loops when you want to test a condition before the first iteration of the loop.

Use do-while loops when you want to test a condition after running the first iteration of the loop.

For example, if you find yourself doing something like either of these snippets:

func();
while (condition) {
   func();
}

//or:

while (true){
    func();
    if (!condition) break;
}

You should rewrite it as:

do{
    func();
} while(condition);

Solution 3:

Difference is that the do loop executes "do something" once and then checks the condition to see if it should repeat the "do something" while the while loop checks the condition before doing anything