Rewriting a for loop as a while/do-while loop

Okay, I know this isn't exactly rocket science but I can't seem to rewrite this for loop to another type of loop:

Code:

---

for (; z != n; n = n->l)
{
      do_something(n);
}

---

The problem is the first condition (at the start) of the for loop is blank, instead of something like for (i = 0; i < 25; i++)... so I'm a little confused as to how the loop works...

z is already defined elsewhere.

Code:

---

for(int i = 1; i < 2; ++i)
{
}

---

is the same as

Code:

---

int i = 1;
for(; i < 2; ++i)
{
}

---

which is the same as

Code:

---

int i = 1;
while(i < 2)
{

//do something
++i;
}

---

In general,

Code:

---

for (init; cond; inc) {
  // loop body
}

---

is equivalent to

Code:

---

init;
while (cond) {
  // loop body
  inc;
}

---

Edit: If init is blank, there's no init. If inc is blank, there's no inc. If cond is blank, then cond is assumed true (so for example for (;;) is an infinite loop).

Edit: Except for the behavior of continue, as K&R2 reminded me. If there's a continue statement in the for loop's body, then inc is executed before the next iteration. In the while loop, that doesn't happen - the next iteration starts immediately.

Thank you very much :) The replies were very useful.

for ( a ; b ; c ) d;

Is almost equivalent to

a;
while ( b ) d ; c ;

Quote:

---

Originally Posted by Salem

for ( a ; b ; c ) d;

Is almost equivalent to

a;
while ( b ) d ; c ;

---

Well, not quite.

Code:

---

a;
while(b) { d; c; }

---

But I understand what you meant.

To be more pedantic: :)

Code:

---

{ //the loop itself is in a separate scope (life-time of the loop counter)
    a;
    while (b)
    { // so is the loop body
        d; c;
    }
}

---

And to incorporate the continue case:

Code:

---

{
  a;
  while(b)
  {
    transformed_d;
    incrementer: c;
  }
}

---

where transformed_d is the sequence of statements in d with each "continue;" replaced by "goto incrementer;"