Question

I’m just curious what peoples’ thoughts are on this topic. Let’s say I have an Array of Objects, and I want to loop through them to see if the Objects contain certain values, and if so, I want to stop the loop. Which is better practice – a for loop with a break, or a conditional loop?

The pseudo-code in the example I have provided is for argument’s sake only (it is also in ActionScript, since that is my primary language of late). Also, I am not looking for best practice ideas on syntax.

for loop with break:

var i:int;  var isBaxterInMilwaukee:Boolean;      for (i = 0; i < arrayLen; i++) {     if (myArray[i]['name'] == 'baxter'          && myArray[i]['location'] == 'milwaukee')     {         isBaxterInMilwaukee = true;          barkTwice();          break;     } } 

conditional loop:

var i:int;  var isBaxterInMilwaukee:Boolean;      while (!isBaxterInMilwaukee && i < arrayLen) {     if (myArray[i]['name'] == 'baxter'          && myArray[i]['location'] == 'milwaukee')     {         isBaxterInMilwaukee = true;          barkTwice();     }      i++; } 

Answer 1

In short, you should go with whichever version is the easiest to read and maintain.

In slightly older times, I know breaking out of a loop was considered to be a no-no (on par with a goto statement). Loops were supposed to break on the loop condition and nowhere else. Thus, the while-loop would have been the way to go.

(This is probably a holdover from assembly, where loops are basically a block of code with a go-to-the-beginning-if-true jump statement at the end. Multiple conditional-jump statements in the block make it exceedingly hard to debug; thus they were to be avoided and combined into one at the end.)

I feel this idea seems to be changing a bit today, especially with foreach loops and the managed world; it’s really a matter of style now. Break-on-found for-loops have perhaps come to be acceptable to many, save some purists of course. Note that I would still avoid using break in a while-loop, however, as this can muddle the loop condition and make it confusing.

If you’ll allow me to use a foreach loop, I consider the code below to be a lot easier to read than its while-loop brother:

bool isBaxterInMilwaukee;      foreach (var item in myArray) {     if (item.name == 'baxter' && item.location == 'milwaukee')     {         isBaxterInMilwaukee = true;             barkTwice();         break;     } } 

However, as the logic grows in complexity, you may want to consider a prominent comment near the break statement lest it become buried and hard to find.

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Arguably, this whole thing should be refactored into its own function which doesn’t break on found, but actually returns the result (feel free to use the for-loop version instead):

bool isBaxterInMilwaukee(Array myArray) {           foreach (var item in myArray)     {         if (item.name == 'baxter' && item.location == 'milwaukee')         {             barkTwice();             return true;         }     }     return false; } 

As Esko Luontola pointed out, it would probably be best to move the call to barkTwice() outside of this function as the side-effect is not evident from the function’s name, nor related to finding Baxter in every case. (Or add a boolean parameter BarkTwiceIfFound and change the line to read if(BarkTwiceIfFound) barkTwice(); to make the side-effect clear.)

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For the record, you can also do the flag check in the for-loop without a break, but I feel this actually hurts readability because you don’t expect an extra condition in a for-loop definition:

var i:int;  var isBaxterInMilwaukee:Boolean;      for (i = 0; !isBaxterInMilwaukee && i < arrayLen; i++) {     if (myArray[i]['name'] == 'baxter'          && myArray[i]['location'] == 'milwaukee')     {         isBaxterInMilwaukee = true;             barkTwice();     } } 

You can also simulate auto-incrementing mechanics with a while-loop. I don’t like this for a few reasons – you have to initialize i to be one less than your real starting value, and depending on how your compiler short-circuits the loop-condition logic, your value of i on exiting the loop may vary. Nevertheless, it is possible and for some people, this can improve readability:

var i:int = -1;  var isBaxterInMilwaukee:Boolean;      while (!isBaxterInMilwaukee && ++i < arrayLen) {     if (myArray[i]['name'] == 'baxter'          && myArray[i]['location'] == 'milwaukee')     {         isBaxterInMilwaukee = true;         barkTwice();     } }