Frequently asked C Programming Questions

Below are the list of some of the questions:

CFAQ:
http://c-faq.com



Some of the good links for Bit Manipulations:
1).  Check if the number is power of two.

If we subtract 1 from a power of 2 what we get is 1s till the last unset bit and if we apply Bitwise AND operator we should get only zeros.

/* Function to check if x is power of 2*/

bool isPowerOfTwo (int x)

{

  /* First x in the below expression is for the case when x is 0 */

  return x && (!(x&(x-1)));

}

2). Check if he number is even of Add using Bitwise operator:

The idea is to check whether the last bit of the number is set or not. If the last bit is set then the number is odd, otherwise even. 

A). bitwise XOR Operation of the Number by 1 increment the value of the number by 1 if the number is even otherwise it decrements the value of the number by 1 if the value is odd.

// Returns true if n is even, else odd

bool isEven(int n)

{

 

    // n^1 is n+1, then even, else odd

    if (n ^ 1 == n + 1)

        return true;

    else

        return false;

}

B).  Biwise And

// Returns true if n is even, else odd

bool isEven(int n)

{

    // n&1 is 1, then odd, else even

    return (!(n & 1));

}

  

c). W know bitwise OR Operation of the Number by 1 increment

the value of the number by 1 if the number is even otherwise

it will remain unchanged.

// Returns true if n is even, else odd

bool isEven(int n)

{

 

    // n|1 is greater than n, then even, else odd

    if ((n | 1) > n)

        return true;

    else

        return false;

} 

3). // C program to check if k-th bit

// of a given number is set or not

#include <stdio.h>

 

void isKthBitSet(int n, int k)

{

    if (n & (1 << (k - 1)))

        printf("SET");

    else

        printf("NOT SET");

}

1).Bit Twiddling Hacks
2).Bitwise Operators from GeekforGeeks

3). 

Strings

Pointers

1. Implementing system calls by yourself (sizeof, strcpy, strcmp etc)
2. Implement your own sizeof and explain
3. 
   
4. 
   

Function Pointers

Structures/Unions/Bit fields/ Structure padding

Memory allocations and APIs (Malloc/calloc/realloc/heap)

 

1. What is the point of using malloc(0)?

Various Keyword (Static, Volatile etc)

1. Can static variables be declared in a header file?
2. Can a variable be both const and volatile?

Make Files

Libraries (Static/Dynamic)

GCC Flags




Some  popular questions:

1. Difference between malloc and new?
2. How will you design interface between two modules?
3. Where variables sits In memory
4. Diff between Vector and list .
5. Volatile keyword
6. Diff between Structure and union 
7. How to get size for union and structure
8. Memory allocation in c
9. Heap or variable which memory is fast
10. Diff between link list and and vector
11. Bit field, how these stored in memory
12. Big endian and little endian
13. If 1000 of integer linklist and array is present which would be faster and why
14. Synchronisation in thread
15. Diff in mutex and binary semaphore
16. C memory management
17. C Storage class
18. Gdb
19. Binary search
20. Multi dimensional array
21. IPC mechanism
22. Which storage class is fast
23. Write your own strtok function where each call return one token separated by delimiter  passed in the string passed. 
24. Reverse string in place. 
25. What are different gcc compiler options to secure your code. 
26. How malloc works behind the scene.
27. How can you protect the same. 
28. What is memory corruption. Different types. 
29. How printf works and write your own printf which can print all basic data type of c. 
30. What is the security issue with printf. 
31. Difference between strlcpy and strncpy. What is the security issue with this. 
32. Check for Balanced parenthesis.

     - using Stack method how you will implement stack and what are different ways. 

     -above algo using lot of memory. now implement same using minimal use of memory.