Question { DOEACC, 6277 }

differnce between do and do while

Answer

The difference between "do while" and "do until" is that a
"do while" loops while the test case is true, whereas "do
until" loops UNTIL the test case is true (which is
equivalent to looping while the test case is false).


The difference between a "do ...while" loop and a "while {}
" loop is that the while loop tests its condition before
execution of the contents of the loop begins; the "do" loop
tests its condition after it's been executed at least once.
As noted above, if the test condition is false as the while
loop is entered the block of code is never executed. Since
the condition is tested at the bottom of a do loop, its
block of code is always executed at least once.

To further clear your concept on this, understand the syntax
and description of the two loop types:

while
The while loop is used to execute a block of code as long as
some condition is true. If the condition is false from the
start the block of code is not executed at al. The while
loop tests the condition before it's executed so sometimes
the loop may never be executed if initially the condition is
not met. Its syntax is as follows.

while (tested condition is satisfied)
{
block of code
}

In all constructs, curly braces should only be used if the
construct is to execute more than one line of code. The
above program executes only one line of code so it not
really necessary (same rules apply to if...else constructs)
but you can use it to make the program seem more
understandable or readable.

Here is a simple example of the use of the while loop. This
program counts from 1 to 100.


#include

int main(void)
{

int count = 1;

while (count <= 100)
{
printf("%d\n",count);
count += 1; // Notice this statement
}

return 0;

}

Note that no semi-colons ( ; ) are to be used after the
while (condition) statement. These loops are very useful
because the condition is tested before execution begins.
However i never seem to like these loops as they are not as
clear to read as the do ...while loops. The while loop is
the favorite amongst most programmers but as for me, i
definitely prefer the do ...while loop.

do ....while
The do loop also executes a block of code as long as a
condition is satisfied.

Again, The difference between a "do ...while" loop and a
"while {} " loop is that the while loop tests its condition
before execution of the contents of the loop begins; the
"do" loop tests its condition after it's been executed at
least once. As noted above, if the test condition is false
as the while loop is entered the block of code is never
executed. Since the condition is tested at the bottom of a
do loop, its block of code is always executed at least once.

Some people don't like these loops because it is always
executed at least once. When i ask them "so what?", they
normally reply that the loop executes even if the data is
incorrect. Basically because the loop is always executed, it
will execute no matter what value or type of data is
supposed to be required. The "do ....while" loops syntax is
as follows

do
{
block of code
} while (condition is satisfied);


Note that a semi-colon ( ; ) must be used at the end of the
do ...while loop. This semi-colon is needed because it
instructs whether the while (condition) statement is the
beginning of a while loop or the end of a do ...while loop.
Here is an example of the use of a do loop.

include

int main(void)
{

int value, r_digit; printf("Enter a number to be
reversed.\n");
scanf("%d", &value); do
{
r_digit = value % 10;
printf("%d", r_digit);
value = value / 10;
} while (value != 0); printf("\n"); return 0;


}

Read more:
http://wiki.answers.com/Q/What_is_the_difference_between_do_while_and_do_until_loop_in_c_programing#ixzz1Uh1xNxCw

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