question about for loop and while loop

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2.33/5 (3 votes)

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C++

void main()

int n=1;

for(;n<5;)
printf("%d",n);
n++;

}

1 can above for loop is similar to while loop? when we initialize control variable before the loop and increment/decrement in the body of the loop

Posted 10-May-12 5:24am

ALIWAZ

Updated 10-May-12 5:40am

Sandeep Mewara

v2

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Sandeep Mewara 10-May-12 11:40am

This is not a well framed question! We cannot work out what you are trying to do/ask from the post. Please elaborate and be specific.
Use the "Improve question" link to edit your question and provide better information.

I added PRE tags to code part to atleast make your content readable.

Code-o-mat 10-May-12 12:06pm

As already said, your question is hard to understand. Anyways, please note that in the code segment you are not increasing the variable 'n' inside of the 'for' loop, since 'n++' isn't in the body of the loop but after it.
e.g:
for (;n<5;)
{
printf("%d",n);
n++;
}
should work better.

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OriginalGriff · Accepted Answer · 2012-05-10T06:02:00

Solution 1

Not quite: Your version would never stop printing - you need "{" and "}" to contain the loop contents, or the first statement only will be looped on.

But:

C++

int i;
for (i = 0; i < 5; i++)
   printf("%d",i);

Is the same as:

C++

int i=0;
while (i < 5)
   {
   printf("%d",i);
   i++;
   }

or:

C#

int i=0;
for (;i < 5;)
   {
   printf("%d",i);
   i++;
   }

But you shouldn't really use the final example.

BTW: It is a good idea to always use curly brackets in a loop of if condition when you are starting to avoid just the kind of problem I mentions at the start!

Posted 10-May-12 6:02am

OriginalGriff

Comments

OriginalGriff 10-May-12 12:23pm

Um. And where in the loop does "n" get incremented?

Code-o-mat 10-May-12 13:56pm

eh, you are right, i have no idea how i mixed that up...will delete my comment to remove the confusement. :) Sorry...

OriginalGriff 10-May-12 13:59pm

It's easy enough to do!
I got caught by it in the days before autoindenting was common, and have stuck with bracketing everything ever since. :laugh:

Code-o-mat 10-May-12 14:15pm

This reminds me of the time long long time ago when i was "headbanging" over a for loop that would only execute once no matter what i tried and i couldn't understand how that was possible, checked all the variables, instructions, increments, everything looked ok but still it wouldn't work. Then i realized there was a damned semicolon at the end of the loop. So something like this, of course the loop i am talking about was a bit...more complex:
int i;
for (i = 0; i < 10; i++);
{
printf("%d\n", i);
}

OriginalGriff 10-May-12 14:25pm

Yep - and it takes forever to spot because you read what you expect to see :O
Did you also bang your head on
if (a = b) {...}
rather than
if (a== b) {...}
because I did! It's one of the reasons I always run with "treat warnings as errors" even now.

Code-o-mat 10-May-12 14:33pm

I usually spot these early on, but yeah, it happened a few times...

Usman Hunjra 10-May-12 14:31pm

Another awesome suggestion ..