11. Difference between pass by reference and pass by value?
Ans: Pass by reference passes a pointer to
the value. This allows the callee to modify the variable directly.Pass by value
gives a copy of the value to the callee. This allows the callee to modify the
value without modifying the variable. (In other words, the callee simply cannot
modify the variable, since it lacks a reference to it.)
12.
What is static identifier?
Ans: A file-scope variable that is declared
static is visible only to functions within that file. A
function-scope or block-scope variable that is declared as static is visible
only within that scope. Furthermore, static variables only have a single
instance. In the case of function- or block-scope variables, this means that
the variable is not “automatic” and thus retains its value across function
invocations.
13. Where is the auto variables stored?
Ans: Auto variables can be stored anywhere,
so long as recursion works. Practically, they’re stored on
the stack. It is not necessary that always a stack exist. You could
theoretically allocate function invocation records from the heap.
14. Where does global, static, and local, register variables, free
memory and C Program instructions get stored?
Ans: Global: Wherever the linker puts them.
Typically the “BSS segment” on many platforms.
Static: Again, wherever the linker puts them. Often, they’re intermixed with
the globals. The only difference between globals and statics is whether the
linker will resolve the symbols across compilation units.Local: Typically on
the stack, unless the variable gets register allocated and never
spills.Register: Nowadays, these are equivalent to “Local” variables. They live
on the stack unless they get register-allocated.
15. Difference between arrays and linked list?
Ans: An array is a repeated pattern of
variables in contiguous storage. A linked list is a set of
structures scattered through memory, held together by pointers in each element
that point to the next element. With an array, we can (on most architectures)
move from one element to the next by adding a fixed constant to the integer
value of the pointer. With a linked list, there is a “next” pointer in each
structure which says what element comes next.
16. What are enumerations?
Ans: They are a list of named
integer-valued constants. Example:enum color { black , orange=4,
yellow, green, blue, violet };This declaration defines the symbols “black”,
“orange”, “yellow”, etc. to have the values “1,” “4,” “5,” … etc. The difference
between an enumeration and a macro is that the enum actually declares a type,
and therefore can be type checked.
17. Describe about storage allocation and scope of global, extern,
static, local and register variables?
Ans:
Globals have application-scope. They’re available in any compilation unit that
includes an
appropriate declaration (usually brought from a header file). They’re stored
wherever the linker puts them, usually a place called the “BSS segment.”
Extern? This is essentially “global.”
Static: Stored the same place as globals,
typically, but only available to the compilation unit that contains them. If
they are block-scope global, only available within that block and its
subblocks.
Local: Stored on the stack, typically. Only
available in that block and its subblocks.
(Although pointers to locals can be passed to functions invoked from within a
scope where that local is valid.)
Register: See tirade above on “local” vs.
“register.” The only difference is that
the C compiler will not let you take the address of something you’ve declared
as “register.”
18. What are register variables? What are the advantages of using
register variables?
Ans: If a variable is declared with a
register storage class,it is known as register variable.The
register variable is stored in the cpu register instead of main
memory.Frequently used variables
are declared as register variable as it’s access time is faster.
19. What is the use of typedef?
Ans: The typedef help in easier
modification when the programs are ported to another machine.
A descriptive new name given to the existing data type may be easier to
understand the code.
20.
Can we specify variable field width in a scanf() format string? If possible
how?
Ans: All
field widths are variable with scanf(). You can specify a maximum field width
for a given
field by placing an integer value between the ‘%’ and the field type specifier.
(e.g. %64s). Such a specifier will still accept a narrower field width.
The one exception is %#c (where # is an integer). This reads EXACTLY #
characters, and it is the
only way to specify a fixed field width with scanf()
