Need to convert this for loop to a while loop

Question

Hi guys,

I solved a problem recently. But I have this one piece of code where I dont utilize the for loop initialization and condition check. It looks a bit odd that way for a for loop. I want to convert it into a while loop. Please help me do it. I tried many times, but somewhere something is missing.

for(;;current =(current+1)%n){
    if(eliminated[current%n]){
        continue;
    }else{
        inkiPinki++;
        if(inkiPinki == m){
            eliminated[current%n] = true;
            printStatus(eliminated, people);
            remainingGuys--;
            break;
        }
    }
}

In the above code eliminiated[index] is a boolean.

Edit: Thanks to Geoff who provided me with a solution which I further minimized like this.

while( eliminated[current] || ++inkiPinki != m )
    current = (current+1) % n;
eliminated[current] = true;
printStatus( eliminated, people );
remainingGuys--;

Answer 1

Try

while( true ) {
    if( !eliminated[current] ) {
        if( ++inkiPinki == m ) {
            break;
        }
    }
    current = (current+1) % n;
}
eliminated[current] = true;
printStatus( eliminated, people );
remainingGuys--;

It should be logically equivalent.

Answer 2

How I would do it:

while (inkiPinki < m) {
    if (!eliminated[current % n]) {
        inkiPinki++;

        if (inkiPinki == m) {
            eliminated[current % n] = true;
        }
    }

    if (inkiPinki < m) {
        current = (current + 1) % n;
    }
}

printStatus(eliminated, people);
remainingGuys--;

This code accomplishes exactly the same thing as your original for loop, except it uses logical tests to determine whether or not it should continue to loop. There's no need for continue or break. If you find yourself using either of these statements, there's probably some refactoring that should be done.

Answer 3

All for loops can be converted to while loops using the following pattern:

for (..xxx..; ..yyy..; ..zzz..) {
  ..aaa..
}

becomes

...xxx...
while (...yyy...) {
  ..aaa..
  ..zzz..
}

remember that

for (;;) {
  ..aaa..
}

is equivalent to

for (nop; true; nop) {
  ..aaa..
}

where "nop" means no operations.

In your example this makes your loop:

for(;;current =(current+1)%n){
    if(eliminated[current%n]){
        continue;
    }else{
        inkiPinki++;
        if(inkiPinki == m){
            eliminated[current%n] = true;
            printStatus(eliminated, people);
            remainingGuys--;
            break;
        }
    }
}

equivalent to

// no initialzation needed
while(true) {
    //if(eliminated[current%n]){
    //    continue;
    //}else{
    if(!eliminated[current%n]){
        inkiPinki++;
        if(inkiPinki == m){
            eliminated[current%n] = true;
            printStatus(eliminated, people);
            remainingGuys--;
            break;
        }
    }
    current =(current+1)%n;
}

From there, you can simplify it further, if you wish.

Answer 4

I seem to have an inordinate fondness for using Booleans as integers:

for (;inkiPinki<m; inkPinki += !eliminated[current])
    current = (current + 1) %n;

eliminated[current] = true;
printStatus(eliminated, people);
remainingGuys--;

I've also changed current%n to simply current in a couple of places, because the %n is already done where current is incremented, so current should already be reduced modulo n.

If I were doing it, I'd probably change the sense, so instead of eliminated, it was something like remaining:

for (;inkiPinki<m; inkPinki += remaining[current])
    current = (current + 1) %n;

remaining[current] = false;
printStatus(remaining, people);
remainingGuys--;