Weird for loop.

I just saw this weird for loop:

Code:

---

#include <stdio.h>
#include <stdlib.h>

main(){
      int i, j;

      for(i=0, j=0; i <= 10; i++, j = i*i){
              printf("i %d j %d\n", i, j);
      }
      printf("Overall: %d\n", ("abc", 1.2e6, 4*3+2));
      exit(EXIT_SUCCESS);
}

---

Please explain it to me, thanks.

what don't you understand about it?

Why did they state 2 variables in that loop and then something like j = i * i and didn't state j in the 2dn paramater..
the whole for loop actually.
why did they printf the variable like this ("abc", 1.2e6, 4*3+2)? wtf?
and what is exit(EXIT_SUCCESS);

I think that either somebody is trying to confuse you, or you're trying to confuse yourself. It's obviously obfuscated code.

The comma operator evaulates the left hand side (lhs) and returns the right hand side (rhs).

Quote:

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and what is exit(EXIT_SUCCESS);

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http://www.cplusplus.com/

what is the comma operator? never heard of it.

it's a comma. You know what a comma is don't you?

Not really.

This is ,

ssharish

Oh.

But why does , relate to the for loop? :O

Code:

---

for(i=0, j=0; i <= 10; i++, j = i*i){

---

To do two things at the same time. I mean u wanted to incr i and i*i at the same time. Thats why. You can do that using the comma operator.

ssharish

I could do the same thing like this:

Code:

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

---

So what's the point?

Quote:

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Originally Posted by eXeCuTeR

I could do the same thing like this:

Code:

---

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

---

So what's the point?

---

Thats true, u reduce the line of instruction by embedding that into for loop ;)

ssharish

Cool, thanks.

BTW,
check out my other thread here (1st page: 'Get source' thread) and help me out please :)

You're allowed to set more than one variable and perform more than one action in a for loop. Recall that a for loop is written like so:

Code:

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for ( initialize; test; action ) {
  [statements]
}

---

Your variables and the actions taken upon them can be the result of pretty much any function call or correct expression, but to do multiple things, the comma operator is used to ensure that they are evaluated, and evaluated in the correct order.

> So what's the point?
The point is, it's useful and not always so abused like in your example. A simple but, unfortunately, trivial example is reversing a C-string with pointers and a for loop.

Code:

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char *head, *tail;
char ch;
for( head = cstr, tail = cstr + strlen( cstr ) - 1; head < tail; ++head, --tail ) {
  ch = *head;
  *head = *tail;
  *tail = ch;
}

---

This doesn't mean that you have to prefer writing this way, but it is a perfectly valid way to use a for loop and you deserve to be aware. Here's some recommended material.

Hey mate, why did you -1 when you strlen(cstr)?

Because I was moving a pointer to the last index of the C-string. If C's arrays started at 1 instead of zero there would be no problem, but they start at zero, so there is. strlen() on a one character string, like "B" for instance, returns 1, not zero, which means that the return result needed to be adjusted for use as an index.