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May 11th, 2009

difference between do and while loops

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What's the main difference between while(){ } and do{ }while() loops? From looking at it, it looks like the former evaluates before it performs the iteration and the latter does the evaluation after each iteration... is that correct? Why would I pick one over the other? Is it mainly just a readability thing? Like

c Syntax (Toggle Plain Text)
bool fail = false;
do{
//something
} while (fail = true);
bool fail = false;
do{
//something
} while (fail = true);

rather than starting fail as true?

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winrawr

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May 11th, 2009

Re: difference between do and while loops

if you want do run a loop at least once, it is better to use do-while loop.
lets explain more. look this sample code:

C Syntax (Toggle Plain Text)
 
FILE *fp;
do
{
    read file and assign some values
}
while( some data in file is equal to special value so file read again );
 
will use last data from file
FILE *fp;
do
{
    read file and assign some values
}
while( some data in file is equal to special value so file read again );

will use last data from file

in this example if you dont use do-while loop structure you need file once before loop and also read in loop

as you say "it is mainly just a readability thing"

Last edited by VatooVatoo; May 11th, 2009 at 4:19 am.

VatooVatoo

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May 11th, 2009

Re: difference between do and while loops

if you want do run a loop at least once, it is better to use do-while loop.
lets explain more. look this sample code:

C Syntax (Toggle Plain Text)
 
FILE *fp;
do
{
    read file and assign some values
}
while( some data in file is equal to special value so file read again );
 
will use last data from file
FILE *fp;
do
{
    read file and assign some values
}
while( some data in file is equal to special value so file read again );

will use last data from file

in this example if you dont use do-while loop structure you need read file once before loop and also read in loop

as you say "it is mainly just a readability thing"

Last edited by VatooVatoo; May 11th, 2009 at 4:20 am.

VatooVatoo

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May 11th, 2009

Re: difference between do and while loops

awesome, thanks

winrawr

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