Thread: About arrays and strings

Arrays in C - Cprogramming.com

Let's look at something new here: the scanf function call is a tad different from what we've seen before. First of all, the format string is '%s' instead of '%d'; this just tells scanf to read in a string instead of an integer. Second, we don't use the ampersand! It turns out that when we pass arrays into functions, the compiler automatically converts the array into a pointer to the first element of the array. In short, the array without any brackets will act like a pointer. So we just pass the array directly into scanf without using the ampersand and it works perfectly.

I tried this with integers instead of string to try understanding what's happening internally.

Code:

#include <stdio.h>


int main( int argc, char *argv[] )  {
	
	int scores[3] = {0,0,0};
	
	printf("\n\nYour scores: ");
	scanf("%d %d %d", scores, scores, scores);
	
	printf("Your scores are: %d %d %d\n\n", scores[0], scores[1], scores[2]);
	
	return 0;
}

Output:

Your scores: 11 14 20
Your scores are: 20 0 0

Code:

printf("Your scores are: %d %d %d\n\n", scores[0], scores[1], scores[2]);

If I remove the brackets [], I get addresses! So, I use "dereferencing" (*) and the output is suddenly 20 20 20.

Originally Posted by camel-man

scores in your scanf is the same thing as saying &scores[0].

The name of an array is just the address to the first element. So when you enter in your numbers you are overriding the first element 3 times. Leaving the first element = to what the last number you entered in at.

I know that and Alex explained that as well:

Arrays in C - Cprogramming.com
compiler automatically converts the array into a pointer to the first element of the array

But my question is beyond that whereby I'm trying to understand how it works when using different things such as plaint scores, &scores, scores[x], &scores[x], *scores and also ptr->scores if I use pointer to a struct. I see the compiler uses different logics when handling an array like the differences between char str[3] and int i[3].

Originally Posted by laserlight

You might want to tweak it a bit to:

Code:

scanf("%d %d %d", scores, scores + 1, scores + 2);

Besides, it will actually be more useful this way

and then use *scores, *(scores+1), *(scores+2) to print it. cool!

now I think the magic resides in the %s, and %c should be the same as %d.

if we pass %s to read and write functions, these functions make use of auto increment while != null character.

Also, remember to check the return value of scanf before proceeding to use what was read by scanf.

I know :

/* Using scanf isn't really the best way to do this; we'll talk about that
in the next tutorial, on strings */

Originally Posted by yvan

I see the compiler uses different logics when handling an array like the differences between char str[3] and int i[3].

There is no difference between char str[3] and int i[3], besides the type of the elements. The syntax and semantics are identical for both.