C Interview Questions 2

8/4/2019 C Interview Questions 2

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Welcome to the

Seminar on C Interview

Questions


2/53

How Would You Print Hello

World on Screen without using anysemi-colons in the code?


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Solution

1. Semi-Colon is the statement terminator in C.

2. Whatre the statements that dont require a semi-colon?

For Instanceif,while.

3. What does printf() return? An int value containing the

number of bytes output.

4. How to embed a printf() within an if() or a while()?


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Solution

int main()

{

if(printf(Hello World)){

}

//while(!printf(Hello World));

}


5/53

What would be the output of:

printf(%c,5[abcdefg]);


6/53

Solution

1. Array Subscripting is Commutative in C.

2. a[e] is identical to *((a)+(e)), for *any* two expressions

a and e, as long as one of them is a pointer expression

and one is integral.

3. Thus,the output for printf(%c,5[abcdefg]); would

be the same as printf(%c,abcdefg[5]);

4. The Output would be: the character at index 5 in the

string abcdefg i.e. f.


7/53

How would you swap the values of

two variables without using a thirdvariable?


8/53

Solution

1. Taking an example:

int a=5,b=2;

a=a+b; // a = 5+2=7, b = 2

b=a-b; // a = 7, b = 7 - 2=5

a=a-b; //a = 7 - 5=2, b=5


9/53

Solution

2. Order of Operations

B = (((A + A) / 2) + (A = B) B);

The trick in this solution is that ((A + A) / 2) yields thevalue A without being stored in the variable A anymore.

So to this we add (A = B), which in turn evaluates to B.

So the total expression has become A + B. To make this

only A, we have to subtract off the extra B.


10/53

What is sizeof('A') ?


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Solution

1. sizeof(A) is the same as sizeof(int).

2. Character constants have type int in C.

3. This is one area where C differs from C++.InC++,sizeof(A)=sizeof(char)


12/53

What's the difference between a

header file and a library?


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Solution

1. A header file typically contains declarations and

definitions, but it never contains executable code.

(A header file arguably shouldn't even contain any

function bodies which would compile into executablecode.)

2. A library, on the other hand, contains only compiled,

executable code and data. A third-party library is oftendelivered as a library and a header file. Both pieces are

important. The header file is included during

compilation, and the library is included during linking.


14/53

What is the difference between

#include and #include file?


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Solution

1. #include

This method of inclusion tells the preprocessor to look

for the file in the predefined default location. It is often

used to include standard headers such as stdio.h or

stdlib.h. This is because these headers are rarely

modified, and they should always be read from your

compilers standard include file directory.


16/53

Solution

2. #include file

This method of inclusion tells the preprocessor to look

for the file in the current directory first, then look for it

in the predefined locations you have set up. The

#include file method of file inclusion is often used toinclude nonstandard header files that you have created

for use in your program. This is because these headers

are often modified in the current directory, and you will

want the preprocessor to use your newly modifiedversion of the header rather than the older, unmodified

version.


17/53

What is the purpose of main( )

function?


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Solution

1. The function main( ) invokes other functions within it.It

is the first function to be called when the program startsexecution.

2. It returns an int value to the environment that called the

program.

3. Recursive call is allowed for main( ) also.

4. It has two arguments 1)argument count and 2) argument

vector (represents strings passed).

Any user-defined name can also be used as parameters

for main( ) instead of argc and argv


19/53

What are command-line arguments?


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Solution

1. Command-Line arguments are the arguments passed to

main() via the command line while executing the

program.

2. int main(int argc,char *argv[])

argc specifies the number of arguments passed.

argv is an array of strings that contains the argumentspassed as strings.


21/53

Solution

3. The first argument i.e. argv[0] always contains the EXE

name.

4. For e.g. if the program EXE is called TEST.EXE and

you execute it like:

C:\>TEST.EXE HELLO WORLD

argc=3

argv[0]=TEST.EXE, argv[1]=HELLO,argv[2]=WORLD


22/53

How much memory space is

occupied by a pointer variable?


23/53

Solution

1. A pointer variable is a variable that may contain the

address of another variable or any valid address in the

memory.

2. Space occupied by a int pointer is the same as that

occupied by a float pointer.

3. Memory occupied by a pointer is 16 bits.


24/53

What is the difference between these

initializations?

char a[] = "string literal";

char *p = "string literal";


25/53

Solution

1. A string literal can be used in two slightly different

ways. As an array initializer (as in the declaration of

char p[]), It specifies the initial values of the characters

in that array.

2. Anywhere else, it turns into an unnamed, static array of

characters, which may be stored in read-only memory,

which is why you can't safely modify it and thus theprogram may crash if you try to change a[i]s value in

the 2nd case i.e. char *p = "string literal";


26/53

What does *p++ increment?


27/53

Solution

1. The ++ operator has higher precedence than the value

at(*) operator.

2. Thus,*p++ increments the pointer p and not the value

pointed to by p.

3. To increment the value of what p points to , use (*p)++;


28/53

What's wrong with...?

char a[]=hello;

if(a==hello)

{//do something }


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Solution

1. Applied to pointers, the == operator compares only

whether the pointers are equal. To compare whether the

strings are equal, you'll have to call strcmp.

2. The if condition would never be true because the value

stored in the array and the string literal its being

compared with,would be stored in different locations.

3. The correct statement would be:

if(strcmp(a,hello)==0) { }


30/53


malloc() and calloc()?


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Solution

1. Both malloc() and calloc() allocate blocks of memory

from the heap. It allows a program to allocate memoryexplicitly as it's needed, and in the exact amounts

needed.

2. The major difference between the two is that whilemalloc() does not set the value of the memory

allocated,calloc() sets the allocated memory to zeroed

bytes.

3. The minor difference is in their syntax:

malloc(10*sizeof(char));

calloc(10,sizeof(char));


32/53

What is the difference between the

stack and the heap?


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Solution

1. The heap is where malloc(), calloc(), and realloc() get

memory. Getting memory from the heap is much slowerthan getting it from the stack. On the other hand, the

heap is much more flexible than the stack. Memory can

be allocated at any time and deallocated in any order.

Such memory isnt deallocated automatically; you have

to call free().

2. If you can keep data in a local variable (and allocate it

from the stack), your code will run faster than if you putthe data on the heap. Sometimes you can use a better

algorithm if you use the heapfaster, or more robust, or

more flexible. If memory is allocated from the heap, its

available until the program ends.

Solution


34/53

Solution

1. The stack is where all the functions local (auto)variables are created. The stack also contains some

information used to call and return from functions.

2. The stack is very inflexible about allocating memory;

everything must be deallocated in exactly the reverse

order it was allocated in. For implementing function

calls, that is all thats needed. Allocating memory off the

stack is extremely efficient. One of the reasons Ccompilers generate such good code is their heavy use of

a simple stack.


35/53

What are function pointers?

Solution


36/53

Solution

1. Function Pointers are pointers, i.e. variables, which

point to the address of a function. You must keep in

mind, that a running program gets a certain space in themain-memory. Both, the executable compiled program

code and the used variables, are put inside this memory.

2. Their declaration is easy: write the declaration as itwould be for the function, say

int func(int a, float b); and simply put brackets around

the name and a * in front of it: that declares the pointer./* pointer to function returning int */

int (*func)(int a, float b);

Solution


37/53

Solution

3. When to use a function pointer?

A very useful application is in replacing a lengthyswitch() statement,or if-else sequences.

Say you want to call a different function for displaying a

letter of the alphabet.Instead of using a switch and 26

cases,you can use an array of function pointers.

void (*fparr[])(void) = {&PrintA(), &PrintB()};

Then,index into this array to call the different functions.fparr[0] to call PrintA(), fparr[1] to call PrintB()


38/53


printf() and sprintf() ?

Solution


39/53

Solution

1. printf prints to the standard output stream stdout,which

is normally the screen.

sprintf() prints to a string.The syntax is the same as

printf but sprintf takes one extra parameter,the string to

write to.

printf(%d,10);

char buffer[10];

sprintf(buffer,%d,10);Note: This is a very simple way to convert numbers to

strings.


40/53

What are storage classes?

Solution


41/53

Solution

A storage class is an attribute that changes the behavior of a

variable. It controls the lifetime, scope and linkage.

There are four types of storage classes :

1)auto 2)static 3)extern 4)register

auto : is the default storage class.The scope and lifetimeof an auto variable is limited to the block in which it is

defined.

static: The scope is limited to the block in which thevariable is declared but the lifetime is the entire

program execution.

Solution


42/53

Solution

register : The register modifier hints to the compilerthat the variable will be heavily used and should be kept

in the CPUs registers, if possible, so that it can be

accessed faster. In fact, many compilers actually ignore

the register modifier, which is perfectly legal, because itis only a hint and not a directive.

extern : The scope of an extern variable extends across

multiple source files and the lifetime is the entireprogram execution.


43/53

What would be the value of i afterthese statements?

int i=5;

sizeof(i++);

Solution


44/53

Solution

1. sizeof does not evaluate the argument passed to it.

2. Thus,the value of i will not change as the i++ instruction

does not get executed.


45/53

How would you print a % with

printf()?


46/53

Solution

1. Why doesnt\% work?

Backslash sequences are interpreted by the compiler

(\n, \", \0, etc.), and \% is not one of the recognized

backslash sequences.

2. printf(%%); is the correct solution.


47/53

How can %f work for type double in

printf if %lf is required in scanf?


48/53

Solution

1. In printf, the "default argument promotions" apply, and

type float is implicitly converted to double. So printf

always receives doubles, and defines %f to be the

sequence that works whether you had passed a float or adouble.

2. scanf, on the other hand, always accepts pointers, and

the types pointer-to-float and pointer-to-double are very

different.No implicit promotions apply.


49/53

How can you you use sizeof to

determine the number of elements inan array?


50/53

Solution

1. Taking an example:

int array[10],size;

size=sizeof(array)/sizeof(array[0]);

2. sizeof(array) returns the total number of bytes occupied

by array.In this case,it returns 10*sizeof(int)

3. To get the number of elements,divide the total numberof bytes by the size of each element of the array.


51/53

What would be the output?

if(a=0) {printf(First);}

if(a=1) {printf(Second);}


52/53

Solution

1. An assignment operation returns the value assigned. i.e.

a=0 returns 0 and a=1 returns 1.

2. The first if condition will never be true since a=0 returns

0 and if(a=0) is the same as if(0).


53/53

How would you write a program in

C that wouldnt compile in C++?

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C Interview Questions 2