Null byte and arrays in C

Question

If I declare a char array of say 10 chars like so...

char letters[10];

am I creating a set of memory locations that are represented as chars fr

Answer 1

Seems like you are confused with arrays and strings.
When you declare

char letters[10] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};  

then it reserves only 10 contiguous bytes in a memory location.

  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  //memory addresses. I assumed it is to be starting from 2000 for simplification. 
 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
 |     |     |     |     |     |     |     |     |     |     |
 | '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' |
 |     |     |     |     |     |     |     |     |     |     |
 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+

In C indexing starts from 0. You can access your allocated memory location from letters[0] to letters[9]. Accessing the location letters[10] will invoke undefined behavior. But when you declare like this

char *letters = "0123456789";  

or

char letters[11] = "0123456789"; 

then there are 11 bytes of space are allocated in memory; 10 for 0123456789 and one for \0 (NUL character).

 2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010 //memory addresses. I assumed it is to be starting from 2000 for simplification. 
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-------+
|     |     |     |     |     |     |     |     |     |     |       |
| '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' | '\0'  |
|     |     |     |     |     |     |     |     |     |     |       |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-------+  
                                                                ^
                                                                | NUL character   

Take another example

#include 

int main(){
   char arr[11];
   scanf("%s", arr);
   printf("%s", arr);

   return 0;
} 

Input:

asdf  

Output:

asdf

Now have a look at memory location

 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-------+
 |     |     |     |     |     |     |     |     |     |     |       |
 | 'a' | 's' | 'd' | 'f' |'\0' |     |     |     |     |     |       |
 |     |     |     |     |     |     |     |     |     |     |       |
 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-------+