while loop question

[ahmad tamimi]

Hello All
I'm new in to java world, i have a question about while loop statement
why we can initialize and declare a variable inside for loop statement, but we cant make the same thing inside while loop statement
for example why we can do the following:
for(int x.....)
but we cant make:
(int x...)
so we should always define var outside the while loop?
Thanks

[Nishan Patel]

I think that is a part of Syntax... may be

[Jhakda Velu]

Hi
The syntax of while loop is

  while(expression){
     doSomething;
}  

The expression should evaluate to a true or false.

Why don't we declare the variable inside?
I quote from the Kathy Sierra book as to why we can't declare the variable used in the condition expression where you pointed

Instead of testing the variable, you'd be declaring
and initializing it, so it would always have the exact same value

Hope that helps, and if it does, mentally thank Kathy(or you can do better, buy the book )

Jhakda

[marten koomen]

The regular for loop is actually similar to a while loop with a number of built in expressions,
that is

for (int i=0;i<3;i++){}

actually has three expressions separated by semicolons, and it does the 'while' checking in the background.

the while loop only has a conditional statement, it's not doing anything else like in a for loop

[Campbell Ritchie]

Welcome to JavaRanch

You may find some more useful information in the Java™ Tutorials.

[Amarnath Pandi]

If you want to initialize and declare a variable inside while loop statement itself why don't you use the for loop itself to serve the purpose?

for(int i=0;i<MAX;){
//Code
i++; //Change the value of i
}

[ahmad tamimi]

Thanks alot for help

[Campbell Ritchie]

Yes, you can do that, but for loops are much easier to understand if you keep to a conventional structure

[Seetharaman Venkatasamy]

ahmad tamimi wrote:
why we can initialize and declare a variable inside for loop statement, but we cant make the same thing inside while loop statement
for example why we can do the following:
for(int x.....)
but we cant make:
(int x...)

That is why many programmer prefer for loop over while loop to avoid cut and paste error since for loop variable's scope is finished within a loop.

[s.palanivel rajan]

Hey first understand the syn taxes clearly...

syntax of FOR loop is

for(initialization;condition;iteration)

ex:for(i=0;i<=10;i++)

syntax for WHILE loop is

while(condition)

even if you use for loop as

for(i<=10;i=0;i++)

we get error message only.. because we don't have any rights to change the syn taxes..
we have to give conditions and initializations in the right places otherwise error will be thrown...

[fred rosenberger]

That is why many programmer prefer for loop over while loop

I'm not sure I agree with this. What I've generally seen is that if you know EXACTLY how many times you need to loop, you would use a for-loop structure. If the number of loops may change from run to run, a while/do-while make more sense.