[SOLVED] why , this for loop is executing infinite times

tushar_pandey · 08-20-2012, 01:21 PM

Code:

for ( ; ; )

why i am saying this because there is no initialization term and no condition and no increment !

colucix · 08-20-2012, 01:32 PM

I'm not an active C programmer, but I remember a simple rule: if any of the three conditions in the for loop is empty, it is evaluated as true. Your example simply brings to an endless loop that doesn't involve any loop variable. Hope this helps.

NevemTeve · 08-20-2012, 05:19 PM

initialization is optional, so is increment. Lack of condition most likely generates a compiler warning, but defaults to non-zero condition, as if it were:

Code:

for ( ; 1; ) ...

tushar_pandey · 08-20-2012, 09:04 PM

Sorry ( colucix & Nevemteve )sir , but i dont understand !

suicidaleggroll · 08-20-2012, 10:21 PM

A for loop without an initialization or increment is just a while loop. In this case, with no conditional the compiler is just setting the conditional to true. So your for loop is essentially just a

Code:

while 1

So it runs forever.

tushar_pandey · 08-21-2012, 03:58 AM

thanks , ( suicidaleggroll )sir , but look at this ,

for ( i = 0 ; i < 5 ; i ++ )

can you please tell me that , initialization portion is executed at once why ! because i know that only static elements are initialized at once !

Celyr · 08-21-2012, 04:18 AM

Quote:

Originally Posted by tushar_pandey

thanks , ( suicidaleggroll )sir , but look at this ,

for ( i = 0 ; i < 5 ; i ++ )

can you please tell me that , initialization portion is executed at once why ! because i know that only static elements are initialized at once !

This is the same as this:

Code:

i=0;
while (i<5)
{
...

i++;
}

NevemTeve · 08-21-2012, 10:36 AM

> can you please tell me that , initialization portion is executed at once why ! because i know that only static elements are initialized at once !

This is another "initialization" it has nothing to do with static/automatic variable-initialization; don't mix these things.

Read this way:

Code:

for (expr1; expr2; expr3) { statements }

Equivalent to:

Code:

expr1; 
while (expr2) {
    statements
    expr3
}

tushar_pandey · 08-22-2012, 01:59 AM

Sir , Nevemteve , now think about this , because when i am trying this , it is running to the infinite times !

Code:

initialization; 
while (condition);  
{
    statements
    increment
}

& sir , please think this thing also for for loop , because for ( ---- ; ---- ; ----- ); , in this why , statements are not executed , because after condition phase statements are processed and after that condition are checked !

TobiSGD · 08-22-2012, 02:02 AM

Quote:

Originally Posted by tushar_pandey

Sir , Nevemteve , now think about this , because when i am trying this , it is running to the infinite times !

Code:

initialization; 
while (condition);  
{
    statements
    increment
}

Without knowing the condition and increment it is impossible to know why (and if) it runs infinitely. If you set up a condition that is always true (may be because your increment is unable to make the condition false) the loop will run infinitely.

tushar_pandey · 08-22-2012, 02:06 AM

Code:

int i = 0 ;
while ( i < 5 ) ;
{

}

and

Code:

int i = 0 ;
while ( i < 5 ) ;
{
       i++ ;
}

, why these two are ::: infinite !

TobiSGD · 08-22-2012, 02:20 AM

Because of the ; after the while command. In your case the command-block of the loop is ended directly after your while statement, the code-block after that is seen as being independent. Remove the ; and the loop will work as intended.
Keep in mind that your first loop will nonetheless run infinitely, since your condition will never be false.

tushar_pandey · 08-22-2012, 02:31 AM

Ok , but still i am not getting your point , now see this ... i am putting your words in for loop !

Code:

for ( i = 0 ; i < 5 ; i ++ );
{
   statement 
}

// now here we have set ";" this , but why statements are not executing , after each and every condition satisfaction !

// because i have use ";" after , incrementing phase and each and every statements in for loop are processed after condition phase !

TobiSGD · 08-22-2012, 02:36 AM

The statements are not executed if you put a ; after the for. If you put a ; after for and while it is for the compiler the same as an invisible empty code-block. So your for command will do 5 times exactly nothing and after that your statement-block is executed one time.
In short:

Code:

for ( i = 0 ; i < 5 ; i ++ );

is the same as

Code:

for ( i = 0 ; i < 5 ; i ++ )
{}

So your example expands to

Code:

for ( i = 0 ; i < 5 ; i ++ )
{}
{
   statement 
}

NateJacobs · 08-22-2012, 04:44 AM

You not to use ";".Use so loop can't go to infinite.

for ( j = 0 ; j < 10 ; j ++ );
{
statement
}