how to check if an array position exist?

Question

char X[3];

how to check if array X[position] exist? for example:

if (x[4] == True)
    printf("Exists")
else 
   printf("NONE")

Answer 1

Each position in a C array, within the array's bounds, always exists, so there's no need for a way to check a random position for existence. All you need to do is make sure that the index is inside the bounds.

If the array is declared with a static size, you can get the length of the array via sizeof:

int array[30];
int length = sizeof(array) / sizeof(int);
// sizeof(array) returns the size in bytes, divide by element size to get element count

However if the array doesn't have a known length at compile time, you'll have to find it out in some other way. C functions dealing with arrays usually take in both a pointer to the first element and the size as separate arguments.

void do_something_to(int *items, int item_count);

You need to be especially careful when passing arrays to functions, since an array passed to a function becomes a "plain pointer" and the compiler loses all track of its size (sizeof will report the size of the pointer). IMHO it's least confusing to avoid array arguments altogether and just stick to pointers.