Thread: String and Pointers

Lets say I have this code,
[code]
void rawr(char *st1);

int main(void) {
char str1[] = "Rawr Rawr Rawr";
rawr(str1);
}

void rawr(char *st1) {

*/How do I grab the first two "rawrs" and make it so that it loops and says things like
/ Rawr
/ awr
/ wr
/ r
/ Thats the output I'm trying to do... just fun
/*


Can anyone help me with this? Reading the online lessons, but pointers and arrays... I dunno. haha, need some help. Any help will be appreciated, thank you.

Originally Posted by dlwlsdn

Lets say I have this code,
[code]
void rawr(char *st1);

int main(void) {
char str1[] = "Rawr Rawr Rawr";
rawr(str1);
}

void rawr(char *st1) {

*/How do I grab the first two "rawrs" and make it so that it loops and says things like
/ Rawr
/ awr
/ wr
/ r
/ Thats the output I'm trying to do... just fun
/*
[/code]

Can anyone help me with this? Reading the online lessons, but pointers and arrays... I dunno. haha, need some help. Any help will be appreciated, thank you.

Code:

void rawr(const char *st1)
{
  for(;*st1;st1++)
    printf("%s\n", st1);
}

Hmm... can you explain that to me please, msater5001. And what does "const" mean (constant?)

and why did you use for(;*st1; st1++)? instead of for(st1=0;*st1;*st1++)?

Sorry, I'm very new to coding.

Code:

void
/*
 * Return nothing
 */

rawr
/*
 * A foolishly named function name.
 */

(
/*
 * The beginning of your parameter list.
 */

const
/*
 * const is like a hot 16 year old. Look but don't touch.
 * You are promising the caller that you will never
 * change the contents of something, but you are going
 * to look at it.
 */

char *
/*
 * This is a pointer to a character sized block of data
 */

st1
/*
 * This is the name of the variable.
 */

)
/*
 * This denotes the end of your parameter list.
 */

{
/*
 * Begin your function definition.
 */

/* Ok, so here is the part that is confusing you the most.
 *
 * You want to start with the string as it is now. So do NOT put
 * st1 = 0; That is just plan wrong.
 *
 * You will move the pointer up one address each time you loop. Which will
 * result in "the next letter" being pointed to.
 *
 * The loop exists once you reach a '\0' character.
 */
  for(;*st1 != '\0';st1++) /* I changed the condition to make it clearer for you */
    printf("%s\n", st1);


}
/*
 * End your function definition.
 */

You are superb... you are godly at C coding. I can see why your called "master"

thanks a lot. You're pretty awesome.

Do you understand pointers very well just yet? If pointers are your area of confusion here, I can certainly show you less pointer-esque ways of doing this. But I won't sugar coat it, any way of doing this requires some pointers and all of them are less efficient than this way.

Hmm, i understand pointers and how they dereference things. And I was wondering about '\0', just making sure, I think I read it somewhere in the lessons. And It was talking about how it means "NULL" or something like that. Just making sure I understand '\0' and pointers. If you think my understanding on pointers and address and stuff like that is drifting in a different way, please let me know.

Thank you for your help again.

0 == '\0'

It is an ascii character. It is the one with a value of zero. It is called NUL. NULL means something a little different. I know its confusing, but I didn't make this stuff up. NUL is a character and NULL means a pointer to nothing.

\0 is less typing than NUL so it sounds like a winner to me

cool, makes sense now. alrighty then. So for(; *s1 != '\0'; s++) and for(; *s1; s++) are the same thing?

Nice. What about writing this part in arrays?

like what i have, which is not

Code:

	int x;
	for(x=0;x;x++)
	{
		printf("%c\n", st1[x]);
		fflush(stdout);

Now, something is wrong here, but I can't get my mind around it. i was wondering if you can help me with that.. Thanks.

You also are doing something fundamentally different in your code. You would be printing

R
a
w
r
\0
... <- garbage until you seg fault...