C questions answers

Sample c questions and answers with explanation for interview

1.
 What will be output if you will compile and execute the following c code?

void main(){

   int i=320;

   char *ptr=(char *)&i;

   printf("%d",*ptr);

}

(A)	320
(B)	1
(C)	64
(D)	Compiler error
(E)	None of above

---

Explanation:

As it is commonly known, the size of the int data type is two bytes, while a char pointer can point to one byte at a time. This difference in size allows for the effective navigation and manipulation of data, with char pointers providing a more granular level of access when needed.

Memory representation of int i=320

So char pointer ptr is pointing to only first byte as shown above figure.

*ptr i.e. content of first byte is 01000000 and its decimal value is 64.

How to represent char, int and float data in memory?

Data type tutorial. 

2.

What will be output if you will compile and execute the following c code?

#define x 5+2

void main(){

    int i;

    i=x*x*x;

    printf("%d",i);

}

(A)	343
(B)	27
(C)	133
(D)	Compiler error
(E)	None of above

---

Explanation:

As commonly understood, the #define preprocessor directive functions as a token-pasting mechanism. It seamlessly incorporates the value of a macro constant directly into the program prior to the commencement of actual compilation. Upon examination of the intermediate file, one would observe:

test.c 1:

test.c 2: void main(){

test.c 3: int i;

test.c 4: i=5+2*5+2*5+2;

test.c 5: printf("%d",i);

test.c 6: }

test.c 7:

You can absorb #define only pastes the 5+2 in place of x in program. So,

i=5+2*5+2*5+2

=5+10+10+2

=27

What is intermediate file and how to see intermediate file?

Preprocessor tutorial.

3.

What will be output if you will compile and execute the following c code?

void main(){

char c=125;

    c=c+10;

    printf("%d",c);

}

(A)	135
(B)	+INF
(C)	-121
(D)	-8
(E)	Compiler error

---

Explanation:

As is widely recognized, the char data type exhibits cyclic properties. When incrementing or decrementing char variables beyond their maximum or minimum values, respectively, they cyclically repeat the same values in accordance with the following cyclic order:

So,

125+1= 126

125+2= 127

125+3=-128

125+4=-127

125+5=-126

125+6=-125

125+7=-124

125+8=-123

125+9=-122

125+10=-121

What is cyclic nature of data type?

Data type tutorial.

4.

What will be output if you will compile and execute the following c code?

void main(){

   float a=5.2;

  if(a==5.2)

     printf("Equal");

  else if(a<5.2)

     printf("Less than");

  else

     printf("Greater than");

}

(A)	Equal
(B)	Less than
(C)	Greater than
(D)	Compiler error
(E)	None of above

---

Explanation:

5.2 is double constant in c. In c size of double data is 8 byte while a is float variable. Size of float variable is 4 byte.

So double constant 5.2 is stored in memory as:

101.00 11001100 11001100 11001100 11001100 11001100 11001101

Content of variable a will store in the memory as:

101.00110 01100110 01100110

It is clear variable a is less than double constant 5.2

Since 5.2 is recurring float number so it different for float and double. Number likes 4.5, 3.25, 5.0 will store same values in float and double data type.

Note: In memory float and double data is stored in completely different way. If you want to see actual memory representation goes to question number (60) and (61).

Data type tutorial.

5.

What will be output if you will compile and execute the following c code?

void main(){

  int i=4,x;

  x=++i + ++i + ++i;

  printf("%d",x);

}

(A)	21
(B)	18
(C)	12
(D)	Compiler error
(E)	None of above

---

Explanation:

In the expression ++a, the ++ symbol represents the pre-increment operator. In mathematical expressions involving this operator, the variable is first incremented up to a breakpoint before assigning the final value to the variable. In the first step, the variable 'a' undergoes incrementation up to the specified breakpoint.

Step 2 involves initiating the assignment of the final value, which is 7, to all variables 'i' within the expression.

So, i=7+7+7=21

What is break point?

Operator tutorial.

6.

What will be output if you will compile and execute the following c code?

void main(){

 int a=2;

 if(a==2){

   a=~a+2<<1;

   printf("%d",a);

 }

 else{

  break;

 }

}

(A)	It will print nothing.
(B)	-3
(C)	-2
(D)	1
(E)	Compiler error

---

Explanation:

The break keyword is not intended for use within an if-else statement. Attempting to include it in such a context will result in a compiler error with the message 'Misplaced break'.

Where we can use break keyword?

Control statement tutorial

7.

What will be output if you will compile and execute the following c code?

void main(){

  int a=10;

  printf("%d %d %d",a,a++,++a);

}

(A)	12 11 11
(B)	12 10 10
(C)	11 11 12
(D)	10 10 12
(E)	Compiler error

---

Explanation:

In C, the printf function follows the cdecl (C declaration) parameter passing scheme. According to this scheme, parameters are passed to a function from right to left direction.

Initially, ++a is processed, incrementing the variable to a value of 10. Subsequently, a++ is executed, resulting in the variable holding a value of 10. Finally, the variable 'a' is accessed directly, bringing its value to 12.

What is cedecl and pascal parameter passing convention?

Function tutorial.

8.

What will be output if you will compile and execute the following c code?

void main(){

   char *str="Hello world";

   printf("%d",printf("%s",str));

}

(A)	11Hello world
(B)	10Hello world
(C)	Hello world10
(D)	Hello world11
(E)	Compiler error

---

Explanation:

The printf function in C returns an integer value equal to the number of characters, including white spaces, that it prints. For instance, printf("Hello, world") will return 12 as there are 12 characters in the provided string.

What is prototype of printf function?

Formatted I/O tutorial.

9.

What will be output if you will compile and execute the following c code?

#include "stdio.h"

#include "string.h"

void main(){

   char *str=NULL;

   strcpy(str,"cquestionbank");

   printf("%s",str);

}

(A)	cquestionbank
(B)	cquestionbank\0
(C)	(null)
(D)	It will print nothing
(E)	Compiler error

---

Explanation:

It's important to note that attempting to use the strcpy function to copy a string to a character pointer pointing to NULL is an invalid operation. This can lead to undefined behavior. Before using strcpy or any string manipulation function, ensure that the destination pointer points to valid and allocated memory with sufficient space for the source string, including the null terminator.

String tutorial.

More questions of string.

10.

What will be output if you will compile and execute the following c code?

#include "stdio.h"

#include "string.h"

void main(){

  int i=0;

  for(;i<=2;)

   printf(" %d",++i);

}

(A)	0 1 2
(B)	0 1 2 3
(C)	1 2 3
(D)	Compiler error
(E)	Infinite loop

---

Explanation:

In for loop each part is optional.

Complete tutorial of looping in C.

11.

What will be output if you will compile and execute the following c code?

void main(){

  int x;

  for(x=1;x<=5;x++);

    printf("%d",x);

}

(A)	4
(B)	5
(C)	6
(D)	Compiler error
(E)	None of above

---

Explanation:

While the body of a for loop is typically enclosed within curly braces {}, it is indeed optional. In this scenario, the for loop will continue to execute until the variable 'x' reaches six, causing the loop condition to evaluate as false.

Looping tutorial.

12.

What will be output if you will compile and execute the following c code?

void main(){

printf("%d",sizeof(5.2));

}

(A)	2
(B)	4
(C)	8
(D)	10
(E)	Compiler error

---

Explanation:

The default type for a floating-point constant in C is double. Consequently, a constant like 5.2 is considered a double constant, and its size is 8 bytes.

Detail explanation of all types of constant in C.

13.

What will be output if you will compile and execute the following c code?

#include "stdio.h"

#include "string.h"

void main(){

char c='\08';

printf("%d",c);

}

(A)	8
(B)	’8’
(C)	9
(D)	null
(E)	Compiler error

---

Explanation:

In C, any character starting with the escape character '\' represents an octal number in character form. However, it's crucial to note that octal digits are limited to 0, 1, 2, 3, 4, 5, 6, and 7. Consequently, the sequence '\08' is an invalid octal character constant due to the presence of the digit '8,' which is not a valid octal digit.

Octal character constantan.

Hexadecimal character constant.

14.

What will be output if you will compile and execute the following c code?

#define call(x,y) x##y

void main(){

int x=5,y=10,xy=20;

printf("%d",xy+call(x,y));

}

(A)	35
(B)	510
(C)	15
(D)	40
(E)	None of above

---

Explanation:

The '##' operator in the C preprocessor is designed for concatenation, exclusively combining its operands. For instance, 'a##b' results in 'ab.' Upon inspecting the intermediate file, you'll observe that the code transforms into the following intermediate code before the commencement of actual compilation.

Intermediate file:

test.c 1:

test.c 2: void main(){

test.c 3: int x=5,y=10,xy=20;

test.c 4: printf("%d",xy+xy);

test.c 5: }

test.c 6:

It is clear call(x, y) has replaced by xy.

What is macro call?

Preprocessor tutorial.

15.

What will be output if you will compile and execute the following c code?

int * call();

void main(){

int *ptr;

ptr=call();

clrscr();

printf("%d",*ptr);

}

int * call(){

int a=25;

a++;

return &a;

}

(A)	25
(B)	26
(C)	Any address
(D)	Garbage value
(E)	Compiler error

---

Explanation:

In this context, the variable 'a' is a local variable with scope and visibility limited to the function call. Once the function returns the address of 'a,' the variable 'a' becomes dead, but the pointer 'ptr' still holds the address of 'a.' This situation is commonly referred to as the dangling pointer problem, where a pointer points to a memory location that may no longer be valid.

Complete pointer tutorial.

16.

What is error in following declaration?

struct outer{

int a;

struct inner{

char c;

};

};

(A)	Nesting of structure is not allowed in c.
(B)	It is necessary to initialize the member variable.
(C)	Inner structure must have name.
(D)	Outer structure must have name.
(E)	There is not any error.

---

Explanation:

At the time of declaration, it is essential to assign a name to an inner structure; otherwise, accessing the members of the inner structure becomes impractical. A correct declaration involves providing a name for the inner structure, as in:

struct outer{

int a;

struct inner{

char c;

}name;

};

Structure tutorial.

Union tutorial.

17.

What will be output if you will compile and execute the following c code?

void main(){

int array[]={10,20,30,40};

printf("%d",-2[array]);

}

(A)	-60
(B)	-30
(C)	60
(D)	Garbage value
(E)	Compiler error

---

Explanation:

In c,

array[2]=*(array+2)=*(2+array)=2[array]=30

Array tutorial.

Array of pointer.

How to read complex pointers.

18.

What will be output if you will compile and execute the following c code?

void main(){

int i=10;

static int x=i;

if(x==i)

printf("Equal");

else if(x>i)

printf("Greater than");

else

printf("Less than");

}

(A)	Equal
(B)	Greater than
(C)	Less than
(D)	Compiler error
(E)	None of above

---

Explanation:

Static variables are associated with load time, whereas auto (automatic) variables are linked to run time. It's important to note that load time variables, such as 'x' in this example, cannot be initialized by run time variables. In the given scenario, 'i' is a run time variable, while 'x' is a load time variable.

What is storage class?

19.

What will be output if you will compile and execute the following c code?

#define max 5;

void main(){

int i=0;

i=max++;

printf("%d",i++);

}

(A)	5
(B)	6
(C)	7
(D)	0
(E)	Compiler error

---

Explanation:

#define is token pasting preprocessor. If you will see intermediate file: test.i

test.c 1:

test.c 2: void main(){

test.c 3: int i=0;

test.c 4: i=5++;

test.c 5: printf("%d",i++);

test.c 6: }

test.c 7:

The macro constant 'max' has been replaced with the value 5. However, attempting to increment a constant value is not allowed, resulting in a compiler error. The error message 'Lvalue required' will be displayed due to the illegal attempt to modify a constant.

What is Lvalue and Rvalue?

How to see intermediate file?

Preprocessor questions and answer.

20.

What will be output if you will compile and execute the following c code?

void main(){

double far* p,q;

printf("%d",sizeof(p)+sizeof q);

}

(A)	12
(B)	8
(C)	4
(D)	1
(E)	Compiler error

---

Explanation:

It is evident that 'p' is a far pointer, and the size of a far pointer is 4 bytes. On the other hand, 'q' is a double variable, and the size of a double variable is 8 bytes.

What is near pointer?

Complete poin

What is far pointer?

What is huge pointer?ter tutorial.

If you have any questions or need clarification regarding the C questions and answers provided above, feel free to ask here. I'm here to help!