C Interview Questions

1 what is the difference between a while statement and a do statement?

Ans: A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once.

2.what is the difference between a break statement and a continue statement?


Ans:A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.

4.how can you tell what shell you are running on unix system?


Ans:You can do the Echo $RANDOM. It will return a undefined variable if you are from the C-Shell, just a return prompt if you are from the Bourne shell, and a 5 digit random numbers if you are from the Korn shell. You could also do a ps -l and look for the shell with the highest PID.


6.How do you print an address?

Ans: The safest way is to use printf() (or fprintf() or sprintf()) with the %P specification. That prints a void pointer (void*). Different compilers might print. a pointer with different formats. Your compiler will pick a format that’s right for your environment. If you have some other kind of pointer (not a void*) and you want to be very safe, cast the pointer to a void*: printf( “%Pn”, (void*) buffer ).

7.Can math operations be performed on a void pointer?


Ans:

No. Pointer addition and subtraction are based on advancing the pointer by a number of elements. By definition, if you have a void pointer, you don’t know what it’s pointing to, so you don’t know the size of what it’s pointing to. If you want pointer arithmetic to work on raw addresses, use character pointers.

8.How can you determine the size of an allocated portion of memory?

Ans:
You can’t, really. free() can , but there’s no way for your program to know the trick free() uses. Even if you disassemble the library and discover the trick, there’s no guarantee the trick won’t change with the next release of the compiler.

9.what is a null pointer?


Ans:
There is times when it’s necessary to have a pointer that doesn’t point to anything. The macro NULL, defined in , has a value that’s guaranteed to be different from any valid pointer. NULL is a literal zero, possibly cast to void* or char*. Some people, notably C++ programmers, prefer to use 0 rather than NULL.

The null pointer is used in three ways:
1) To stop indirection in a recursive data structure
2) As an error value
3) As a sentinel value.

10.Is NULL always defined as 0?

Ans:
NULL is defined as either 0 or (void*)0. These values are almost identical; either a literal zero or a void pointer is converted automatically to any kind of pointer, as
Necessary, whenever a pointer is needed (although the compiler can’t always tell when a pointer is needed).