It appears that the return value from printf (the number of characters output) becomes the return value of main. Not all systems exhibit this property.
7.2
When the program is run interactively, standard output is usually line buffered, so the actual output occurs when each newline is output. If standard output were directed to a file, however, it would probably be fully buffered, and the actual output wouldn't occur until the standard I/O cleanup is performed.
7.3
On most UNIX systems, there is no way to do this. Copies of argc and argv are not kept in global variables like environ is.
7.4
This provides a way to terminate the process when it tries to dereference a null pointer, a common C programming error.
7.5
The definitions are
typedef void Exitfunc(void); int atexit(Exitfunc *func);
7.6
calloc initializes the memory that it allocates to all zero bits. ISO C does not guarantee that this is the same as either a floating-point 0 or a null pointer.
7.7
The heap and the stack aren't allocated until a program is executed by one of the exec functions (described in Section 8.10).
7.8
The executable file (a.out) contains symbol table information that can be helpful in debugging a core file. To remove this information, the strip(1) command is used. Stripping the two a.out files reduces their size to 381,976 and 2,912 bytes.
7.9
When shared libraries are not used, a large portion of the executable file is occupied by the standard I/O library.
7.10
The code is incorrect, since it references the automatic integer val through a pointer after the automatic variable is no longer in existence. Automatic variables declared after the left brace that starts a compound statement disappear after the matching right brace.
