Thread: C int pointers

I'm learning C and have a question about this code:

Code:

#include <stdio.h>

int main() {

char date[]   = "20091005";

char year[5]  = "YYYY";
char month[3] = "MM";
char day[3]   = "DD";

char *my_pointer = date;

year[0] = *(my_pointer);
year[1] = *(my_pointer + 1);
year[2] = *(my_pointer + 2);
year[3] = *(my_pointer + 3);

month[0] = *(my_pointer + 4);
month[1] = *(my_pointer + 5);

day[0] = *(my_pointer + 6);
day[1] = *(my_pointer + 7);

printf("The Year is: %s and the Month is: %s and the Day is: %s  ", year, month, day);

return 0;
}

I changed it to this (changes marked in bold):

Code:

#include <stdio.h>

int main() {

int date[]   = 20091005; /* Removed quotes and changed char to int */

int year[5]  = 2009; /* Removed quotes, changed char to int, and changed YYYY to 2009 */
int month[3] = 10; /* Removed quotes, changed char to int, and changed MM to 10 */
int day[3]   = 05; /* Removed quotes, changed char to int, and changed DD to 05 */

int *my_pointer = date; /* Changed char to int */

year[0] = *(my_pointer);
year[1] = *(my_pointer + 1);
year[2] = *(my_pointer + 2);
year[3] = *(my_pointer + 3);

month[0] = *(my_pointer + 4);
month[1] = *(my_pointer + 5);

day[0] = *(my_pointer + 6);
day[1] = *(my_pointer + 7);

printf("The Year is: %d and the Month is: %d and the Day is: %d  ", year, month, day); /* Changed %s to %d */

return 0;
}

But it wouldn't compile due to this error:

Code:

practice1.c: In function 'main':
practice1.c:5: error: invalid initializer
practice1.c:7: error: invalid initializer
practice1.c:8: error: invalid initializer
practice1.c:9: error: invalid initializer

Why can I not use int instead of char for the pointer?

Okay I just realized 20091005 is just a really big number 20,091,005. Even if I change that data type to 'unsigned double long' or something I guess it wouldn't make a difference but I still don't understand why I need to represent these numbers as characters.

Okay, so this code compiled fine:

Code:

#include <stdio.h>

int main() {

int date[]  = {20091005};

int year[5]  = {2009};
int month[3] = {10};
int day[3]   = {05};

int *my_pointer = date;

year[0] = *(my_pointer);
year[1] = *(my_pointer + 1);
year[2] = *(my_pointer + 2);
year[3] = *(my_pointer + 3);

month[0] = *(my_pointer + 4);
month[1] = *(my_pointer + 5);

day[0] = *(my_pointer + 6);
day[1] = *(my_pointer + 7);

printf("The Year is: %d and the Month is: %d and the Day is: %d \n", year, month, day);

return 0;
}

But the results are:

Code:

$ a.out                                                         
The Year is: -809539600 and the Month is: -809539568 and the Day is: -809539580 
$

Isn't it:

date[] = [2][0][0][9][1][0][0][5][\0] (9 array spots)

year[5] = [2][0][0][9][\0]
month[3] = [1][0][\0]
day[3] = [0][5][\0]

Or am I understanding this incorrectly?

Since you changed things to int arrays, it's totally broken.
year[0], year[1] is meaningless the way you meant it. What are you trying to do? Extract the digits?

*(my_pointer + 1) etc is wrong. You don't have an array of dates to begin with. At least the elements of which are not defined.

Originally Posted by guitarscn

Okay, so this code compiled fine:

"Compiled" does not equal "works".

Or am I understanding this incorrectly?

Unfortunately I'd have to say you are way way off base here...

What exactly are you trying to accomplish?