NULL operator

[RyanC]

why can't we use in pointers *p=0? we should put instead of 0 another expression that express to 0 which is NULL, is NULL defined in C itself as nothing like '/0'?, meaning if I write for example

a[5]={3,4,5,6,7}
if a[6]=='NULL' 
     printf("the elements of the array is finished")

thanks in advance.

[RyanC]

More over, when do we use typedef ? and what does it stand for?

[Click_here]

nul '\0' and NULL are very different.
"One L is an ASCII key, two L's point to nothing"

FAQ > NULL, 0, \0 and nul? - Cprogramming.com

[GReaper]

Wowowow, one step at a time.

The reason you can't(implicitly) terminate an array with a "NULL" element is because C is really direct about its types. An int is an int, a float is a float, a pointer to struct is a pointer to struct. Nothing less, nothing more.

In order to do what you want, which is possible with C but not preferable, you'll have to declare the array as an array of pointers. That way, the last one could be NULL.

Now, typedef is used to define a new type, as the name implies. It's mostly used to shorten or customize other types/structs:

typedef unsigned char BYTE;
typedef struct
{
    int value;
}foo;

BYTE aByte = 255;
foo aFoo = { 123456 };

[Matticus]

FAQ > NULL, 0, \0 and nul? - Cprogramming.com
http://c-faq.com/null/nullor0.html

I know you just posted an example, but accessing "a[6]" in your array brings you to the land of undefined behavior. The only valid indices of "a[5]" are 0 through 4.

Also, NULL should not be enclosed in single quotes.