Another way to use continue keyword in C++

Question

Recently we found a "good way" to comment out lines of code by using continue:

for(int i=0; i<MAX_NUM; i++){
  ....
  .... //--> about 30 lines of code
  continue;
  ....//--> there is about 30 lines of code after continue
  ....
}

I scratch my head by asking why the previous developer put the continue keyword inside the intensive loop. Most probably is he/she feel it's easier to put a "continue" keyword instead of removing all the unwanted code...

It trigger me another question, by looking at below scenario:

Scenario A:

for(int i=0; i<MAX_NUM; i++){
  ....
  if(bFlag)
    continue;
  ....//--> there is about 100 lines of code after continue
  ....
}

Scenario B:

for(int i=0; i<MAX_NUM; i++){
  ....
  if(!bFlag){
  ....//--> there is about 100 lines of code after continue
  ....
  }
}

Which do you think is the best? Why? How about break keyword?

Answer 1

Using continue in this case reduces nesting greatly and often makes code more readable.

For example:

for(...) {
    if( condition1 ) {
        Object* pointer = getObject();
        if( pointer != 0 ) {
            ObjectProperty* property = pointer->GetProperty();
            if( property != 0 ) {
        ///blahblahblah...
        }
     }
}

becomes just

for(...) {
    if( !condition1 ) {
        continue;
    }
    Object* pointer = getObject();
    if( pointer == 0 ) {
        continue;
    }
    ObjectProperty* property = pointer->GetProperty();
    if( property == 0 ) {
       continue;
    }

    ///blahblahblah...
}

You see - code becomes linear instead of nested.

You might also find answers to this closely related question helpful.

Answer 2

For your first question, it may be a way of skipping the code without commenting it out or deleting it. I wouldn't recommend doing this. If you don't want your code to be executed, don't precede it with a continue/break/return, as this will raise confusion when you/others are reviewing the code and may be seen as a bug.

As for your second question, they are basically identical (depends on assembly output) performance wise, and greatly depends on design. It depends on the way you want the readers of the code to "translate" it into english, as most do when reading back code.

So, the first example may read "Do blah, blah, blah. If (expression), continue on to the next iteration." While the second may read "Do blah, blah, blah. If (expression), do blah, blah, blah"

So, using continue of an if statement may undermine the importance of the code that follows it.

In my opinion, I would prefer the continue if I could, because it would reduce nesting.