Null pointer: A pointer which doesn’t points at a memory location is known as a null pointer. It is generally used to mark the end of a pointer array. For Example, this loop will encounter a null pointer:
for(i=0; p[i]; ++i)
String table: A string table is created by a compiler to store string constants used by the program. For Example:
char *a = “More Process”;
Here, address of More Process is stored in the string table.