when a while loop will stop ?

what is the condition for the while loop to be invalid ?

i think the following are the condition for invalid while loop.


1. while(false ) // bool false --> loop will stop


2. while(NULL) ----> loop will stop

3. while(0) ----->loop will stop

4. while('\0') -----> loop will stop.


i think there are many more conditions like above... so there are basically different rules.

is there any other condition which can make the while loop stop ?

Anything that reduces to a boolean false will stop a while loop, thus...

while ( 1 == 2 )

... will do. The other examples you give, (some of which may or may not work with all compilers), are simply examples of this.

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The other examples you give, (some of which may or may not work with all compilers), are simply examples of this.

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can u tell which are the doubtfill examples ? i have not found those in the book. looking some codes i have listed out those conditions.

The while loop is pretty simple. If the expression results in any non-zero value, it will continue. If it results in zero, then it will end. Thats all there is to it. There are no doubtful exceptions. If its zero, it stops, period.

Don't forget you can also use break; to end the loop

Or a goto or a return or an exit().

well... I don't think anyone should use goto, it messes up the code.

Yea, I'm not even sure how, but I've always thought that 'goto' is bad coding.

you can make a while loop run for a few cycles then stop. IE:

Code:

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int j = 1;
while (j <= 10)
 {
  printf("The loop has cycled %d time//s", j);
  j++;
 }

---

The loop will run 10 times. It adds 1 to j each cycle until J is greater than 10 and the condition is false (which returns 0).

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can u tell which are the doubtfill examples ?

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Yea,
while(false) wont work because it will look for a variable named false.
while(NULL) wont work because it will look for a constant called NULL.

I hope this has helped.
-=Wynter=-

PS: I know I've been coding C to long because while typing this, I puntuated a sentince with a semicolon rather than a period. =]

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you can make a while loop run for a few cycles then stop

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It's nice when you know for how long it should loop. But what if you don't know. You're then using an endless loop, an endless loop that you only want to stop if something fails...

You have two "normal" ways to do that:

the first is by using an extra variable to know when to stop:

Code:

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int stop=0;

while (!stop) {
  if (something1()==NULL)
      stop = 1;
  else if (something2()==NULL)
      stop = 1;

  . . .
}

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and the second way (the better way, if you ask me), by breaking the while loop:

Code:

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while (1) {    // or for (;;), same thing.
  if (something1()==NULL)
      break;
  if (something2()==NULL)
      break;

  . . .
}

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as you can see, with break you save a variable, and the code looks much better.

More correctly it will look for an object named false or NULL which of course could be anything.

Things can be doubtful only if you don't look at it in context.

Code:

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while ( !IamATrueReturingFunction() );

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Now this might look like it would never go into the loop but if the function was actually

Code:

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int IamATrueReturingFunction(void){return 0;}

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then it becomes a theoritical infinate loop.

Code:

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while (1) {    // or for (;;), same thing.
  if (something1()==NULL)
      break;
  if (something2()==NULL)
      break;

  . . .
}

---

Or you can be a little smarter and do:

Code:

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while ( something1() != NULL && something2() != NULL ) {
  . . .
}

---

While breaks are very nice a lot of times they can be used for poor structuring.

But but if it's something like that:
(and I don't want to put it all in a single function and then call only that function.)

Code:

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while ( something1(var1, var2, var3, var4)
            && something2(var1, var2, var3, var4)
            && something3(var1, var2, var3, var4)
            && something4(var1, var2, var3, var4)
            && something5(var1, var2, var3, var4) )
{
...
}

---

nice mess, don't you think.

Quote:

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While breaks are very nice a lot of times they can be used for poor structuring

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define poor structuring.

Quote:

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define poor structuring.

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IMO using an infinte loop and breaks.

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nice mess, don't you think.

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Not really. Seen much much much worse.

I was reading Stroustrup's book and he gave his personal opinon that he doesn't like do while loops because then you don't know he exit condition when you start the loop. While I don't agree 100% with this, I do believe that the exit condition(s) should be fairly clear in inside the while() or for(). IMO breaks (in loops) should be used for the "oh crap" situations or when you need to break out of the loop in the middle of the loop. If the breaks are at the beginning or the end of the loop then there is a problem.

I do agree that using endless loops is not the best idea, but sometimes it's the only one... I remember writing vga dos games in highschool (don't ask why :)) and I had to use an endless loop as the main loop for the game.


Also, I usually only use break when I deal with endless loops and the switch() statement.

but I still don't see what's so wrong with using break everytime I want to stop a loop?