Style question about existing piece of code (C/C++)

Question

I just hope the following doesn't seem to you like redundant jabber :)
Anyway, there is that:

for (p = fmt; *p; p++) {
    if (*p != '%') {
        putchar(*p);
        continue;
    }
    switch (*++p) {
        /* Some cases here */
        ...
    }
 }

And I wondered why the writer (Kernighan / Ritchie) used the continue in the if statement.
I thought it was for the mere reason that he deemed it would be more elegant than indenting the whole switch under an else statement, what do you think?

Answer 1

Probably. The human brain has limited stack space, making it difficult to deal with deeply nested structures. Anything that flattens the information we're expected to parse makes it easier to understand.

Similarly, I normally prefer this:

bool foo(int arg)
{
    if(!arg) {
        /* arg can't be 0 */
        return false; 
    }

    /* Do some work */
    return true;
 }

To this:

 bool foo(int arg) 
 { 
     if(!arg) {
         /* arg can't be 0 */ 
         return false; 
     } else {
         /* Do some work */ 
         return true;
     } 
 }

Or worse, to this:

bool foo(int arg) 
{ 
    if(arg) {
        /* Do some work */ 
        return true;
    } else {
        /* arg can't be 0 */ 
        return false; 
    } 
}

In the last example, the part that does the work might be quite long. By the time the reader gets to the else clause, he may not remember how he got there.

Putting the bail out conditions as close to the beginning helps to assure that people who try to call your functions will have a good idea of what inputs the function expects.

Also, as others pointed out, the continue makes it clear that there's no need to read further into the code inside the loop to determine whether any more processing is done after that point for this case, making the code easier to follow. Again, the fewer things you force the reader to keep track of, the better.