Top 80 C-Language Interview Questions and Answers

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Top 80
C Programming
Interview Questions and Answers

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ANSWER
What is C language?
C is a structured, procedural programming language that has been widely used both for
operating systems and applications and that has had a wide following in the academic
community.
QUESTION 1
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ANSWER
Who invented C language?
In 1972, Dennis Ritchie developed a new language by combining features from BCPL and
B and adding some additional features naming the language as C.
QUESTION 2

ANSWER
What are the features of C language?
• The C compiler combines the capabilities of an assembly language with features of a
high-level language.
• Programs Written in C are efficient and fast. This is due to its variety of data type and
powerful operators.
• C is highly portable this means that programs once written can be run on another
machines with little or no modification.
• Another important feature of C program, is its ability to extend itself.
QUESTION 3

ANSWER
What are the uses of C language?
C is often used for "system programming", including implementing operating
systems and embedded system applications, due to a combination of desirable
characteristics such as code portability and efficiency.
QUESTION 4

ANSWER
What do you mean by a Constant?
Constants are also like normal variables. But, only difference is, their values can’t be
modified by the program once they are defined.
• They refer to fixed values
• They are also called as literals
• They may be belonging to any of the data type
QUESTION 5

ANSWER
What are the Rules of constructing constants?
• An integer constant must have at least one digit
• It must not have a decimal point
• It can either be positive or negative
• No commas or blanks are allowed within an integer constant
• A real constant must have at least one digit
• The maximum length of a character constant is 1 character
QUESTION 6

ANSWER
What do you mean by a Variable?
• Variables are simply names used to refer to some location in memory a location that
holds a value with which we are working.
• It may help to think of variables as a placeholder for a value.
• You can think of a variable as being equivalent to its assigned value.
QUESTION 7

ANSWER
What are the rules for naming a C variable?
• Variable name must begin with letter or underscore
• Variables are case sensitive
• They can be constructed with digits, letters
• No special symbols are allowed other than underscore
• Sum, height, _value are some examples for variable name
QUESTION 8

ANSWER
What are data types? Name the different types of data types in C language.
Data types are defined as the data storage format that a variable can store a data to
perform a specific operation.
Types of data types:
• Basic data types- int, char, float, double
• Enumeration data type- enum
• Derived data type- pointer, array, structure, union
• Void data type- void
QUESTION 9

ANSWER
What is the purpose of the String() function?
C Strings are nothing but array of characters ended with null character (‘0’). This null
character indicates the end of the string. Strings are always enclosed by double quotes.
QUESTION 10

ANSWER
What do you mean by tokens and keywords?
• Tokens are the basic buildings blocks in C language which are constructed together to
write a C program. Each and every smallest individual units in a C program are known
as Tokens.
• Keywords are pre-defined words in a C compiler. Each keyword is meant to perform a
specific function in a C program.
QUESTION 11

ANSWER
What is the difference between constant and volatile keyword?
Constants are also like normal variables. But, only difference is, their values can’t be
modified by the program once they are defined.
• They refer to fixed values
• They are also called as literals
When a variable is defined as volatile, the program may not change the value of the
variable explicitly.
• These variable values might keep on changing
• They have no explicit assignment to the program
QUESTION 12

ANSWER
What are the different types of operators?
C language offers many types of operators. They are:
1. Arithmetic operators
2. Assignment operators
3. Relational operators
4. Logical operators
5. Bit wise operators
6. Conditional operators
7. Special operators
QUESTION 13

ANSWER
What is the difference between operators and expressions?
• An operator is a symbol that tells the compiler to perform specific mathematical or
logical manipulations.
• An expression is a combination of explicit values, constants, variables, operators,
and functions that are interpreted according to the particular rules of precedence.
QUESTION 14

ANSWER
What is a loop?
Loops are used to repeat a block of code. Being able to have your program repeatedly
execute a block of code is one of the most basic but useful tasks in programming - many
programs or websites that produce extremely complex output are really only executing
a single task many times.
QUESTION 15

ANSWER
What are the rules for constructing a identifier name in C?
• The first character of the variable name must either be alphabet or underscore
• No commas and blanks are allowed in the variable name
• No special symbols other than underscore are allowed in the variable name
• Avoid creating long variable name as it adds to your typing effort
QUESTION 16

ANSWER
What is syntax error?
Syntax error is a mistake in the syntax of some strange sequence of characters
or tokens that is intended to be stated in a particular programming language.
QUESTION 17

ANSWER
What is a local block?
A local block is any portion of a C program that is enclosed by the left brace ({) and the
right brace (}). A C function contains left and right braces, and therefore anything
between the two braces is contained in a local block. An if statement or
a switch statement can also contain braces, so the portion of code between these two
braces would be considered a local block.
QUESTION 18

ANSWER
Should variables be stored in local block?
The use of local blocks for storing variables is unusual and therefore should be avoided,
with only rare exceptions. One of these exceptions would be for debugging purposes,
when you might want to declare a local instance of a global variable to test within your
function. You also might want to use a local block when you want to make your program
more readable in the current context.
QUESTION 19

ANSWER
When is switch statement better than multiple if statements?
Switch statement is generally best to use when you have more than two conditional
expressions based on a single variable of numeric type.
QUESTION 20

ANSWER
Can the last case of a switch statement skip including the break?
Even though the last case of a switch statement does not require a break statement at
the end, you should add break statements to all cases of the switch statement, including
the last case. You should do so primarily because your program has a strong chance of
being maintained by someone other than you who might add cases but neglect to
notice that the last case has no break statement.
QUESTION 21

ANSWER
What is the difference between goto and long jmp( ) and setjmp()?
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.
QUESTION 22

ANSWER
What is a rvalue?
rvalue can be defined as an expression that can be assigned to an lvalue.
The rvalue appears on the right side of an assignment statement.
QUESTION 23

ANSWER
Can an array be an 1value?
The answer to this question is no, because a n array is composed of several separate
array elements that cannot be treated as a whole for assignment purposes.
QUESTION 24

ANSWER
When is the "void" keyword used in a function?
• The void keyword allows you to define a function that returns no data.
• Functions that do not return any value are sometimes referred to as procedures or
subroutines.
• The sub keyword is an alias for void.
• Both of these keywords can only be used when declaring or defining a function.
QUESTION 25

ANSWER
What are the difference between malloc() and calloc()?
• Calloc is used to allocate a block of memory, the allocated region is initialized to
zeroes.
• Malloc does not touch the contents of the allocated block of memory, which means it
contains garbage values.
QUESTION 26

ANSWER
Is the left to right or right to left order gauranteed for operator precedence?
The simple answer to this question is neither. The C language does not always evaluate
left-to-right or right-to-left. Generally, function calls are evaluated first, followed by
complex expressions and then simple expressions.
QUESTION 27

ANSWER
Specify the different types of decision control statements in C.
• If
• If else
• Nested if
QUESTION 28

ANSWER
What are the advantages of using pointers?
• Pointers are more efficient in handling arrays and data tables
• They can be used to return multiple values from a function via function arguments
• Pointers permit references to functions
• Pointers allow C to support dynamic memory management
• Pointers reduce length and complexity of programs
QUESTION 29

ANSWER
What is a static variable?
A static variable is a variable that has been allocated statically—whose lifetime or
"extent" extends across the entire run of the program.
QUESTION 30

ANSWER
What is the difference between declaring a variable and defining a variable?
• When you declare a variable, a function, or even a class all you are doing is saying:
there is something with this name, and it has this type.
• Defining something means providing all of the necessary information to create that
thing in its entirety.
QUESTION 31

ANSWER
Where is an auto variable stored?
They are stored in main memory. Memory is allocated to an automatic variable when
the block which contains it is called and it is de-allocated at the completion of its
block execution.
QUESTION 32

ANSWER
How are errors handled in C language?
• C programming does not provide direct support for error handling but being a system
programming language, it provides you access at lower level in the form of return
values.
• C programmer can check the returned values and can take appropriate action
depending on the return value.
• Developer should set error to 0 at the time of initialization of the program.
QUESTION 33

ANSWER
What do you mean by a storage class? Name the storage classes which can be used in a
C Program?
A storage class in C is an attribute that tells us where the variable would be stored, what
will be the initial value of the variable if no value is assigned to that variable.
Four types of storage classes are:
• Automatic storage class
• Register storage class
• Static storage class
• External storage class
QUESTION 34

ANSWER
What are the rules for constructing identifier name in C.
Rules for constructing identifier name in C:
• First character should be an alphabet or underscore
• Succeeding characters might be digits or letter
• Punctuation and special characters aren’t allowed except underscore
• Identifiers should not be keywords
QUESTION 35

ANSWER
What are case control statement? Name the types of case control statements in C
language.
The statements which are used to execute only specific block of statements in a series of
blocks are called case control statements.
There are 4 types of case control statements in C language. They are:
• switch
• break
• continue
• goto
QUESTION 36

ANSWER
What is the scope of register and static variables?
• Register is used to define local variables that should be stored in a register instead of
RAM.
• Static is the default storage class for global variables. The two variables count and road
both have a static storage class.
QUESTION 37

ANSWER
What is the use of printf and scanf function?
• printf() function is used to print the “character, string, float, integer, octal and
hexadecimal values” onto the output screen.
• scanf() function is used to read character, string, numeric data from the keyboard.
QUESTION 38

ANSWER
What is debugging?
Debugging is the process of locating and fixing or bypassing bugs (errors) in computer
program code or the engineering of a hardware device.
QUESTION 39

ANSWER
What is FIFO and LIFO?
• FIFO (first-in, first-out) is an approach to handling program work requests from queues
or stacks so that the oldest request is handled next.
• LIFO (last-in, first-out) is an approach in which the most recent request is handled next
and the oldest request doesn't get handled.
QUESTION 40

ANSWER
What is the && operator and how does it function in a program code?
• The && is also known as AND operator and returns the boolean value true if both
operands are true and returns false.
• The operands are implicitly converted to type bool prior to evaluation, and the result
is of type bool.
• Logical AND has left-to-right associativity.
QUESTION 41

ANSWER
What is the difference between “break” and continue statements?
• The break statement is used to exit the current loop before its normal ending.
• The continue statement resumes iteration of a
enclosing for, while, until or select loop.
QUESTION 42

ANSWER
Elaborate the buffer manipulation function?
• Buffer manipulation functions in C work on the address of the memory block rather
than the values inside the address.
• Example programs for memset(), memcpy(), memmove(), memcmp(), memicmp() and
memchr() functions are given below.
QUESTION 43

ANSWER
What is call by reference in functions?
• The call by reference method of passing arguments to a function copies the address of
an argument into the formal parameter.
• Inside the function, the address is used to access the actual argument used in the call.
QUESTION 44

ANSWER
Which is a better option in C Language – Macros or Functions?
Macros are more faster and efficient as compared to functions but complex
programming cannot be handled by macros so whether to use macros or functions
depends on the priority as well as use.
QUESTION 45

ANSWER
What is a memory leak? How can it be avoided?
• Memory leak occurs when programmers create a memory in heap and forget to
delete it.
• To avoid memory leaks, memory allocated on heap should always be freed when no
longer needed.
QUESTION 46

ANSWER
What is gets( ) function?
In the C Programming Language, the gets function reads characters from
the stdin stream and stores them in s. The gets function returns s.
QUESTION 47

ANSWER
What do you mean by a nested loop?
• A nested loop is a loop within a loop, an inner loop within the body of an outer one.
• How this works is that the first pass of the outer loop triggers the inner loop, which
executes to completion. Then the second pass of the outer loop triggers the
inner loop again.
QUESTION 48

ANSWER
What is Dynamic memory allocation in C? Name the dynamic allocation functions.
• The process of allocating memory during program execution is called dynamic
memory allocation.
C language offers 4 dynamic memory allocation functions:
• malloc()
• calloc()
• realloc()
• free()
QUESTION 49

ANSWER
What are the uses of Static local variables?
• Static variables declared at block scope are initialized the first time control passes
through their declaration.
• On all further calls, the declaration is skipped.
QUESTION 50

ANSWER
What do you mean by Modular Programming?
Modular programming is a software design technique that emphasizes separating the
functionality of a program into independent, interchangeable modules, such that each
contains everything necessary to execute only one aspect of the desired functionality.
QUESTION 51

ANSWER
What are Unions and what does it reflect in C?
• Union is a user defined data type. In union, all members share the same memory
location.
• For example in the following C program, both x and y share the same location.
QUESTION 52

ANSWER
What are the applications of Unions?
• Unions can be useful in many situations where we want to use same memory for two
ore more members.
• For example, suppose we want to implement a binary tree data structure where each
leaf node has a double data value, while each internal node has pointers to two
children, but no data.
QUESTION 53

ANSWER
What is the difference between “Char a” and “Char a[1]”?
• “char a” represents a character variable and “char a[1]” represents a char array of size
1.
• If we print value of char a, we get ASCII value of the character (if %d is used). And if we
print value of char a[1], we get address of the only element in array.
QUESTION 54

ANSWER
What do you understand by enumerations?
• The process of allocating memory during program execution is called dynamic
memory allocation.
• An enumeration is a user-defined type that consists of a set of named integral
constants that are known as enumerators.
QUESTION 55

ANSWER
What are macros? What are the advantages and disadvantages of macros?
A macro is a way to automate a task or procedure which you perform on a regular basis.
• Advantage: A large number of task or action can be recorded in a single macro
• Disadvantage: If something needs to be changed in the macro, the whole macro must
be re-recorded
QUESTION 56

ANSWER
What are Arrays? Name the types of C arrays.
Array is a collection of variables belongings to the same data type. You can store group
of data of same data type in an array.
Types of C arrays:
• One dimensional array
• Multi dimensional array
QUESTION 57

ANSWER
What is typedef?
• typedef is a keyword in the C and C++ programming languages.
• The purpose of typedef is to form complex types from more-basic machine types and
assign simpler names to such combinations.
QUESTION 58

ANSWER
What is the difference between strings and arrays?
• Array is a collection of variables belongings to the same data type. You can store group
of data of same data type in an array.
• String is traditionally a sequence of characters, either as a literal constant or as some
kind of variable.
QUESTION 59

ANSWER
What is generic pointer in C?
When a variable is declared as being a pointer to type void it is known as a generic
pointer.
QUESTION 60

ANSWER
What do you understand by a function?
• A function is a group of statements that together perform a task.
• Every C program has at least one function, which is main(), and all the most trivial
programs can define additional functions.
QUESTION 61

ANSWER
What is hashing?
• Hashing is the transformation of a string of characters into a usually shorter fixed-
length value or key that represents the original string.
• Hashing is used to index and retrieve items in a database.
QUESTION 62

ANSWER
What techniques are used for debugging?
Techniques used for debugging:
• Use compiler’s features
• Read the fine module
• Printf ( ) debugging
• Code grinding
• Assertion
QUESTION 63

ANSWER
Do you know pragma directive in C?
The Pragma directive is the method specified by the C standard for providing additional
information to the compiler, beyond what is conveyed in the language itself.
QUESTION 64

ANSWER
What is the output of printf(“%d”)?
When we write printf(“%d”) the compiler will print the value of x. But as there is nothing
after %d so compiler will show in output window garbage value.
QUESTION 65

ANSWER
Can include files be nested?
Yes. Include files can be nested any number of times. As long as you use precautionary
measures, you can avoid including the same file twice.
QUESTION 66

ANSWER
How many levels deep can include files be nested?
• Even though there is no limit to the number of levels of nested include files you can
have, your compiler might run out of stack space while trying to include high number
of files.
• This number varies according to your hardware configuration and possibly your
compiler.
QUESTION 67

ANSWER
What are compilers?
A compiler is a computer program that transforms source code written in
a programming language into another computer language (the target language, often
having a binary form known as object code).
QUESTION 68

ANSWER
What is #line used for?
#line lets you modify the compiler's line number and (optionally) the file name output
for errors and warnings.
QUESTION 69

ANSWER
What is the benefit of using enum to declare a constant?
The main benefit of using enum is that if you don't initialize your constants, each one
would have a unique value. The first would be zero and the rest would then count
upwards.
QUESTION 70

ANSWER
What is the difference between printf() and sprintf()?
• Sprintf() writes data to the character array.
• Printf() writes data to the standard output device.
QUESTION 71

ANSWER
How can we reduce the file size of executable?
The file size of executable can be reduced with the help of dynamic linking for libraries.
QUESTION 72

ANSWER
What is a stack?
Stack is an area of memory that holds all local variables and parameters used by any
function, and remembers the order in which functions are called so that function
returns occur correctly.
QUESTION 73

ANSWER
What are the four types of stack in C?
Four types of stack in C are:
• Block scope
• Function scope
• File scope
• Program scope
QUESTION 74

ANSWER
Where are command line arguments given?
Command-line arguments are given after the name of a program in command-line
operating systems like DOS or Linux, and are passed in to the program from the
operating system.
QUESTION 75

ANSWER
What is nested structure?
Structure written inside another structure is called as nesting of two structures.
QUESTION 76

ANSWER
When should the volatile modifier be used?
The volatile modifier is a directive to the compiler’s optimizer that operations involving
this variable should not be optimized in certain ways.
QUESTION 77

ANSWER
What is a file header?
• A header file is a file with extension .h which contains C function declarations and
macro definitions and to be shared between several source files.
• There are two types of header files: the files that the programmer writes and the files
that come with your compiler.
QUESTION 78

ANSWER
What is Type casting?
Type casting is a way to convert a variable from one data type to another data
type. For example, if you want to store a long value into a simple integer then
you can type cast long to int.
QUESTION 79

ANSWER
What do you mean by Recursion and recursive call of the function?
Recursion is the process of repeating items in a self-similar way. Same applies in
programming languages as well where if a programming allows you to call a function
inside the same function that is called recursive call of the function as follows.
QUESTION 80

• http://www.cprogramming.com
• http://ecomputernotes.com/what-is-c
• http://www.tutorialspoint.com/cprogramming/
• http://fresh2refresh.com/c
• http://searchwindowsserver.techtarget.com/definition/C
• http://www.studytonight.com/c
• en.wikibooks.org/wiki/C_Programming/Variables
• http://www.cprogramming.com/tutorial/c
• http://www.learnconline.com
• http://www.indiabix.com/technical/c/the-c-language-basics
• http://ecomputernotes.com/what-is-c
• http://www.programming-techniques.com
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Top 80 C-Language Interview Questions and Answers