for loop in c programming

Hey, here is something you should know: Those thingies separated by ';' characters in the head of the for loop are expressions, all three of them! Both for loops compile but this should give a warning: for(i=0;i++;i<5) because the last expression doesn't have a side effect (ie: it does not change anything) and your compiler is smart! As I said all three thingies are expressions but the first is used for initialization, the second is for pre-testing before every execution of the loop-body, and the third expression is executed after each execution of the loop-body.

This c code:

for (expr1; expr2; expr3)
{
   code_in_the_body_of_for_loop
}

Can be written this way:

expr1            // initialization, like i=0; the compiler should warning if this
                 // has no side effect (if it doesnt change anything like i<5)

while (1)        // infinite loop
{
    if (!expr2)  // pre testing before execution of the loop-body
        break;

                 // this is the code inside the for loop, note that
                 // a "continue" statement in the body of the  for loop
                 // jumps to expr3 and not to the beginning of the for loop!!!
    code_in_the_body_of_for_loop

    expr3;       // usually some expressions that change the loop-counter
                 // like i++ or i+=5 or ptr = ptr->parent;
                 // the compiler should warning if this has no side effect.
}

In your case when the pre-test expression (expr2) is i++ the for loop never executes the body code because the value of i++ is zero so it breaks out from your for loop immediately! You compiler should also warning if expr3 is just i<5 because you normally never write a statement like i<5; in your code, do you? :D