two different loops, are they doing the same thing ?

venix · 12-03-2009, 01:35 PM

Loop 1:

Code:

for (int i =1 ; array[i]!=0; i++) 
		if (&array[i] == block) 
		{
			
			printf("array[i] = %d\n ", array[i]);
			printf("array[i+1]= %d\n", array[i+1]);
			printf("array[i-1]= %d\n", array[i-1]);
			position = i;
			blockSize = *block;
			break;
		}

Loop 2:

Code:

int i =1;
  while(array[i]!=0)
  i++;
	if (&array[i] == block) 
	{
		printf("array[i] = %d\n ", array[i]);
		printf("array[i+1]= %d\n", array[i+1]);
		printf("array[i-1]= %d\n", array[i-1]);
		position = i;
		blockSize = *block;
	}

are this achieve the same thing ? if not what are the difference in the output?

pixellany · 12-03-2009, 01:41 PM

Why not run them both and find out????

What is the context of this?

smeezekitty · 12-03-2009, 01:43 PM

Quote:

Originally Posted by pixellany

Why not run them both and find out????

LOL Yeah.

Quote:

What is the context of this?

Homework, i'm sure.

jaydot · 12-03-2009, 01:54 PM

i'm no programmer, but it looks to me like one is for a one-off print and the second for more than one print.

with 'while' in the second, so long as the stated condition is true, churn out another print.

if it is homework, i can help lead you far, far astray.

venix · 12-03-2009, 02:02 PM

Quote:

Originally Posted by smeezekitty

LOL Yeah.

Homework, i'm sure.

Do you want my code to check it out ? it will take you 1 week and 3 days to find out

pixellany · 12-03-2009, 04:14 PM

Quote:

Originally Posted by venix

Do you want my code to check it out ? it will take you 1 week and 3 days to find out

Now that you have exchanged your little jabs, how about answering my question: Run the 2 programs and see what they do.

ntubski · 12-03-2009, 04:28 PM

Quote:

Originally Posted by venix

are this achieve the same thing ?

No, Loop 2 won't compile since it is missing some punctuation.

Quote:

if not what are the difference in the output?

Loop 2 can't give output since it can't run.

venix · 12-03-2009, 06:03 PM

Quote:

Originally Posted by ntubski

No, Loop 2 won't compile since it is missing some punctuation.

Loop 2 can't give output since it can't run.

this is not a homework. Is one part of homework that i came up while trying to make mymalloc() function , where did you see the missing punctuation ?

graemef · 12-03-2009, 07:37 PM

There is quite a bit of difference between the two, but it is impossible to tell if the differences are intentional or not. Maybe you could explain a little more about why you are asking your question and what happened when you ran the code.

GazL · 12-03-2009, 08:30 PM

Quote:

Originally Posted by graemef

There is quite a bit of difference between the two, but it is impossible to tell if the differences are intentional or not.

fixed his indentation and it looks something like this...

Code:

int i =1;
while(array[i]!=0)   /*  1  */
   i++;

if (&array[i] == block)  /*  2  */
{
   printf("array[i] = %d\n ", array[i]);
   printf("array[i+1]= %d\n", array[i+1]);
   printf("array[i-1]= %d\n", array[i-1]);
   position = i;
   blockSize = *block;   /*  3  */
}

increase element index number 'i' until array element contents is zero
compare pointer 'block' to address of array element i
if equal, set blockSize from contents of array element pointed to by pointer block, which is pointing to array element i (*2*), which contains 0 (*1*)

Unless I'm reading it wrong (which is possible as I'm a bit rusty with C), blockSize will only ever get set to 0.

I suspect the differences are not intentional and it's just plain broken.

bamboo789 · 12-03-2009, 08:40 PM

I think they are missing { and } ,is right?
They are have some differece:
code1:
print array[i],array[i-1] and array[i+1] first,then i++

code2:
i++ first and then print array,so the results of printting is not same. And the value of positon are different too.The first one is less than the second one,I think.

GazL · 12-03-2009, 09:24 PM

Yep, I think you're right bamboo, it makes a little more sense if he's missed out a whole { } block on that while, but there are still logic difference in there.

increasing i at the start means that &array[1] is never checked against block, so that'd need fixing for starters.

graemef · 12-03-2009, 09:50 PM

Reading the code the indentation implies that the while is missing the braces, but the break in the for loop could imply that the looping should stop when the if condition is met, meaning that the while condition should have consisted of two conditions!

Yes the incrementing of the loop counter in the while loop is wrong, if the braces are missing but again are the braces really meant to be there?

As I said without knowing the intent of the code it is not possible to be any more precise.

Dogs · 12-03-2009, 10:29 PM

Awesome.. I can tell that reading The C Programming Language has done something.. I saw the issue(s) before I read the the rest of the thread..

I dunno why no one has answered the question yet, but far be it for me to break the silence.

pintodragon · 12-04-2009, 06:57 AM

Quote:

Originally Posted by venix

Loop 1:

Code:

for (int i =1 ; array[i]!=0; i++) 
		if (&array[i] == block) 
		{
			
			printf("array[i] = %d\n ", array[i]);
			printf("array[i+1]= %d\n", array[i+1]);
			printf("array[i-1]= %d\n", array[i-1]);
			position = i;
			blockSize = *block;
			break;
		}

Loop 2:

Code:

int i =1;
  while(array[i]!=0)
  i++;
	if (&array[i] == block) 
	{
		printf("array[i] = %d\n ", array[i]);
		printf("array[i+1]= %d\n", array[i+1]);
		printf("array[i-1]= %d\n", array[i-1]);
		position = i;
		blockSize = *block;
	}

are this achieve the same thing ? if not what are the difference in the output?

If you did indeed want Loop 2 to do the if and printf's inside the while loop then no the two loops do not do the same thing.

Loop 2 will start looking at &array[2] and check if that is == to block. If you are going to use a while loop to iterate through an array in place of a for loop then you should put the i++ after your last usage of it. So an updated Loop 2 would be:

Code:

  int i =1;
  while(array[i]!=0)
  {
    if (&array[i] == block) /* First time through i is now 1 not 2 */
    {
        printf("array[i] = %d\n ", array[i]);
        printf("array[i+1]= %d\n", array[i+1]);
        printf("array[i-1]= %d\n", array[i-1]);
        position = i;
        blockSize = *block;
    }	
    i++;
  }