C interview questions - Part 2

Please share it with your friends who are preparing for interview , and comment down your suggestions , or any mistake in the post. 

code snippets are hosted on ideone.com. you can run code there as well.

1. What will be new average given ( old average + number of samples ) and new sample value :

New average = ( old average ) * ( old number of samples ) + new sample / ( old number of samples + 1 ) 

2. Read some details about C standard libraries : 

< https://www.tutorialspoint.com/c_standard_library/ >

3. Remeber that strings are terminated with null character "\0" (zero) , this is how we find end of the string. In C language there is no seperate string data type , strings are created using arrays. Where as in C++ , strings are a seperate class.

also '\0'( ASCII ) is 0x00 in hex.

'0'( ASCII ) is 0x30 in hex.

one interesting string question < https://stackoverflow.com/questions/18688971/c-char-array-initialization/18688992#18688992 >

Consider below example of "strlen" vs "sizeof" below.

4. What is use of Assert for error handling in C language ???

C assert() statement is a runtime assert statement i.e it won't give you a compile time error , but it will result into runtime error when assert() statement fails.

Compile time asserts can be also written , using preprocessor directives like #if , #warning, #error or using if...else. Always remember preprocessor is invoked before compiler and linker.

Please play around with below example code , I would recommend to install codeblocks + MinGW in yout machine and try there.

5. What is use of Cygwin ( note : windows bash is going to replace Cygwin ).

< https://www.quora.com/For-what-purposes-is-cygwin-exactly-used >

6. Overflow of smaller data type:

Remeber that when you assign a "larger value" to a "smaller data type variable" overflow occurs.

Also remember that range of signed char is -128 to 127 ( negative side is more ) and unsigned char range is 0 to 255.

< https://stackoverflow.com/questions/21667971/what-happens-when-a-char-is-assigned-a-value-too-large-to-fit-in-a-byte >

consider following example :

7. Rules of integer promotion  and type casting in C :

This is excellent article.

< https://www.geeksforgeeks.org/integer-promotions-in-c/ >

also try this code as well:

Is integer promotion always needed ? 

< https://stackoverflow.com/questions/12807953/do-integer-promotions-always-happen-when-evaluating-an-expression >

8. Types of Error in C :

There are 3 types of errors : compile time , link time , run time , logical/design errors.

compile time error can be syntex error or semantic error.

It's very difficult to detect design errors.

< https://www.geeksforgeeks.org/errors-in-cc/ >

example of sematic error :

int main(void) {

    volatile unsigned int temp;

    10 = temp;

}

error: lvalue required as left operand of assignment.

9. what is lvalue and rvalue ??

< https://www.geeksforgeeks.org/lvalue-and-rvalue-in-c-language/ >

10. How would you avoid invalid use of assignment operator instead of comparison operator ??

consider below nasty situation and try to guess output :

to avoid this you can make rule to write VALUES/rvalue on left hand side of comparision operator. as writng rvalue on left hand side of assignment operator will result in simantic error.

You should write following way.

11. Write a code to convert big Endian to little endian and vice versa :

I found this very optimised in terms of memory < https://www.tutorialspoint.com/how-do-i-convert-between-big-endian-and-little-endian-values-in-cplusplus >

< https://www.geeksforgeeks.org/bit-manipulation-swap-endianness-of-a-number/ >

12. operator precedence in c :

while it is better to us brackets to isolate statements in C , knowledge of operator precedence is necessary to avoid unnecessary use of brackets.

< https://www.geeksforgeeks.org/operator-precedence-and-associativity-in-c/ >

< https://www.geeksforgeeks.org/evaluation-order-of-operands/ >

13. Dividend ÷ Divisor = Quotient ( and reminder ) , numerators and denominators.

remember that % will take the sign of dividend ( this is reminder ) 

14. Duff's device:

< https://en.wikipedia.org/wiki/Duff's_device >

15. coroutine vs subroutine vs threads :

< https://stackoverflow.com/questions/1934715/difference-between-a-coroutine-and-a-thread >

< https://stackoverflow.com/questions/24780935/difference-between-subroutine-co-routine-function-and-thread >

16. write a program to find a number is power of 2 :

here the trick is number 2 , note that if a given number is power of 2 then that number will have only 1 bit set in it's binanry representation. 

< https://www.geeksforgeeks.org/program-to-find-whether-a-no-is-power-of-two/ >

17. Write a generic program to find if  given number "pow" is power of number "num":

This cannot be achived by the technique above. And you have to go traditional way of dividing numbers or multiplying the numbers and then comparing them.

18. Write a C program to swap all nibbles in individual byte in an 32-bit integer.

< https://stackoverflow.com/questions/3649026/how-to-display-hexadecimal-numbers-in-c >

19. Write a macro to define a register variable in C.

< https://stackoverflow.com/questions/18785991/define-regx-volatile-unsigned-int-x > 

20. what is stack overflow and heap overflow ?

< https://www.geeksforgeeks.org/heap-overflow-stack-overflow/ >

21. does malloc always returns contiguous memory ?

Answer is YES.

< https://stackoverflow.com/questions/625270/does-malloc-allocate-a-contiguous-block-of-memory >

Others :

I would strongly recommend to read SO anweres of this account.

< https://stackoverflow.com/users/1119701/ouah >

Please share it with your friends who are preparing for interview , and comment down your suggestions , or any mistake in the post. 

code snippets are hosted on ideone.com. you can run code there as well.