Example of a while loop that can't be written as a for loop

Question

I know a while loop can do anything a for loop can, but can a for loop do anything a while loop can?

Please provide an example.

Answer 1

Using C

The basic premise is of the question is that while loop can be rewritten as a for loop. Such as

init;
while (conditional) {
  statement;
  modify;
}

Being rewritten as;

for ( init; conditional; modify ) {
  statements;
}

The question is predicated on the init and modify statements being moved into the for loop, and the for loop not merely being,

init;
for (; conditional; ) {
  modify;
}

But, it's a trick question. That's untrue because of internal flow control which statements; can include. From C Programming: A Modern Approach, 2nd Edition you can see an example on Page 119,

n = 0;
sum = 0;
while ( n < 10 ) {
  scanf("%d", &i);
  if ( i == 0 )
    continue;
  sum += i;
  n++;
}

This can not be rewritten as a for loop like,

sum = 0;
for (n = 0; n < 10; n++ ) {
  scanf("%d", &i);
  if ( i == 0 )
    continue;
  sum += i;
}

Why because "when i is equal to 0, the original loop doesn't increment n but the new loop does.

And that essentially boils down to the catch,

Explicit flow control inside the while loop permits execution that a for loop (with internal init; and modify; statements) can not recreate.