C Interview Questions and Answers

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(Continued from previous part...)

Is it acceptable to declare/define a variable in a C header?

A global variable that must be accessed from more than one file can and should be declared in a header file. In addition, such a variable must be defined in one source file.
Variables should not be defined in header files, because the header file can be included in multiple source files, which would cause multiple definitions of the variable. The ANSI C standard will allow multiple external definitions, provided that there is only one initialization. But because there’s really no advantage to using this feature, it’s probably best to avoid it and maintain a higher level of portability.
Global variables that do not have to be accessed from more than one file should be declared static and should not appear in a header file.

Why should I prototype a function?

A function prototype tells the compiler what kind of arguments a function is looking to receive and what kind of return value a function is going to give back. This approach helps the compiler ensure that calls to a function are made correctly and that no erroneous type conversions are taking place.

What is the quickest searching method to use?

A binary search, such as bsearch() performs, is much faster than a linear search. A hashing algorithm can provide even faster searching. One particularly interesting and fast method for searching is to keep the data in a digital trie. A digital trie offers the prospect of being able to search for an item in essentially a constant amount of time, independent of how many items are in the data set.
A digital trie combines aspects of binary searching, radix searching, and hashing. The term digital trie refers to the data structure used to hold the items to be searched. It is a multilevel data structure that branches N ways at each level.

What are the advantages of auto variables?

1)The same auto variable name can be used in different blocks
2)There is no side effect by changing the values in the blocks
3)The memory is economically used
4)Auto variables have inherent protection because of local scope

What are the characteristics of arrays in C?

1) An array holds elements that have the same data type
2) Array elements are stored in subsequent memory locations
3) Two-dimentional array elements are stored row by row in subsequent memory locations.
4) Array name represents the address of the starting element
5) Array size should be mentioned in the declaration. Array size must be a constant expression and not a variable.

How do you print only part of a string?

/* Use printf() to print the first 11 characters of source_str. */
printf(First 11 characters: ‘%11.11s’n, source_str);

In C, what is the difference between a static variable and global variable?

A static variable declared outside of any function is accessible only to all the functions defined in the same file (as the static variable). However, a global variable can be accessed by any function (including the ones from different files).

In C, why is the void pointer useful?

When would you use it? The void pointer is useful becuase it is a generic pointer that any pointer can be cast into and back again without loss of information.

(Continued on next part...)

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