C FAQS
Q:What is a pointer variable?
Ans:A pointer variable is a variable that may contain the address of
another variable or any valid address in the memory.
Q:What is a pointer value and address?
Ans:A pointer value is a data object that refers to a memory location.
Each memory location is numbered in the memory. The number attached to a
memory location is called the address of the location.
Q:What is a modulus operator? What are the restrictions of a modulus
operator?
Ans:A Modulus operator gives the remainder value. The result of x%y is
obtained by (x-(x/y)*y). This operator is applied only to integral operands
and cannot be applied to float or double.
Ans:A linker converts an object code into an executable code by linking
together the necessary build in functions. The form and place of declaration
where the variable is declared in a program determine the linkage of variable.
Q:What is a function and built-in function?
Ans:A large program is subdivided into a number of smaller programs or
subprograms. Each subprogram specifies one or more actions to be performed for
a large program. such subprograms are functions.
The function supports only static and extern storage classes. By default,
function assumes extern storage class. functions have global scope. Only
register or auto storage class is allowed in the function parameters. Built-in
functions that predefined and supplied along with the compiler are known as
built-in functions. They are also known as library functions
What is a macro, and how do you use it?
A macro is a preprocessor directive that provides a mechanism for token
replacement in your source code. Macros are created by using the #define
statement.
Here is an example of a macro: Macros can also utilize special operators such
as the stringizing operator (#) and the concatenation operator (##).The
stringizing operator can be used to convert macro parameters to quoted
strings, as in the following example:
#define DEBUG_VALUE(v) printf(#v is equal to %d.n, v)
In your program, you can check the value of a variable by invoking the
DEBUG_VALUE macro:
...
int x = 20;
DEBUG_VALUE(x);
...
The preceding code prints x is equal to 20. on-screen. This example shows that
the stringizing operator used with macros can be a very handy debugging tool.
Q:What is the difference between goto and longjmp() and setjmp()?
Ans:A goto statement implements a local jump of program execution,
and the longjmp() and setjmp() functions implement a nonlocal, or far, jump of
program execution.
Generally, a jump in execution of any kind should be avoided because it is not
considered good programming practice to use such statements as goto and
longjmp in your program.
A goto statement simply bypasses code in your program and jumps to a
predefined position. To use the goto statement, you give it a labeled position
to jump to. This predefined position must be within the same function. You
cannot implement gotos between functions.
When your program calls setjmp(), the current state of your program is saved
in a structure of type jmp_buf. Later, your program can call the longjmp()
function to restore the program’s state as it was when you called
setjmp().Unlike the goto statement, the longjmp() and setjmp() functions do
not need to be implemented in the same function.
However, there is a major drawback to using these functions: your program,
when restored to its previously saved state, will lose its references to any
dynamically allocated memory between the longjmp() and the setjmp(). This
means you will waste memory for every malloc() or calloc() you have
implemented between your longjmp() and setjmp(), and your program will be
horribly inefficient. It is highly recommended that you avoid using functions
such as longjmp() and setjmp() because they, like the goto statement, are
quite often an indication of poor programming practice.
Q:Is it acceptable to declare/define a variable in a C header?
Ans:A global variable that must be accessed from more than one file can
and should be declared in a header file. In addition, such a variable must be
defined in one source file.
Variables should not be defined in header files, because the header file can
be included in multiple source files, which would cause multiple definitions
of the variable. The ANSI C standard will allow multiple external definitions,
provided that there is only one initialization. But because there’s really no
advantage to using this feature, it’s probably best to avoid it and maintain a
higher level of portability.
Global variables that do not have to be accessed from more than one file
should be declared static and should not appear in a header file.
Q:Why should I prototype a function?
Ans:A function prototype tells the compiler what kind of arguments a
function is looking to receive and what kind of return value a function is
going to give back. This approach helps the compiler ensure that calls to a
function are made correctly and that no erroneous type conversions are taking
place.
Q:What is the quickest searching method to use?
Ans:A binary search, such as bsearch() performs, is much faster than a
linear search. A hashing algorithm can provide even faster searching. One
particularly interesting and fast method for searching is to keep the data in
a digital trie. A digital trie offers the prospect of being able to search for
an item in essentially a constant amount of time, independent of how many
items are in the data set.
A digital trie combines aspects of binary searching, radix searching, and
hashing. The term digital trie refers to the data structure used to hold the
items to be searched. It is a multilevel data structure that branches N ways
at each level.
Q:What are the advantages of auto variables?
Ans:1)The same auto variable name can be used in different blocks
2)There is no side effect by changing the values in the blocks
3)The memory is economically used
4)Auto variables have inherent protection because of local scope
Q:What are the characteristics of arrays in C?
Ans:1) An array holds elements that have the same data type
2) Array elements are stored in subsequent memory locations
3) Two-dimensional array elements are stored row by row in subsequent memory
locations.
4) Array name represents the address of the starting element
5) Array size should be mentioned in the declaration. Array size must be a
constant expression and not a variable.
