C Programming Interview Question and Answer SET 8

141. Do you know, what is the meaning and use of static keyword in c?

Keyword static is used for declaring static variables in c. This modifier is used with all data types like int, float, double, array, pointer, structure, function etc.

142. What is difference between .com program and .exe program?

Both .com and .exe program are executable program but .com program execute faster than .exe program. All drivers are .com program. .com file has higher preference than .exe For example:

143. Difference between TSR and TSO program

TSO means terminate but stay outside. It is that program, which release the main memory after the execution of the program. Example ms paint, notepad, turbo c compilers etc.

TSR means terminate but stay residence .It is those program, which after the execution of the program does not release the RAM (main memory).e.g. antivirus.

144. Describe turbo c compiler?

Turbo c is an IDE of c programming language created by Borland. Turbo C 3.0  is based on MS DOS operation  system. It is one of the most popular c compilers. It uses 8086 microprocessor which is 16 bit microprocessor. It has 20 address buses and 16 data bus. Its word length is two byte.

145. Out of fgets() and gets() which function is safe to use and why?

fgets() is safer than gets(), because we can specify a maximum input length. Neither one is completely safe, because the compiler can’t prove that programmer won’t overflow the buffer he pass to fgets ().

146. Difference between strdup and strcpy?

Both copy a string. strcpy wants a buffer to copy into. strdup allocates a buffer using malloc().
Unlike strcpy(), strdup() is not specified by ANSI .

147. Differentiate between a for loop and a while loop? What are it uses?

For executing a set of statements fixed number of times we use for loop while when the number of
iterations to be performed is not known in advance we use while loop.

148. What is storage class? What are the different storage classes in C?
Storage class is an attribute that changes the behavior of a variable. It controls the lifetime, scope and linkage. The storage classes in c are auto, register, and extern, static, typedef.

149. What are the uses of a pointer?

(i)It is used to access array elements
(ii)It is used for dynamic memory allocation.
(iii)It is used in Call by reference
(iv)It is used in data structures like trees, graph, linked list etc.

150.In header files whether functions are declared or defined?

Functions are declared within header file. That is function prototypes exist in a header file,not function bodies. They are defined in library (lib).

151. Difference between pass by reference and pass by value?

Pass by reference passes a pointer to the value. This allows the callee to modify the variable directly.Pass by value gives a copy of the value to the callee. This allows the callee to modify the value without modifying the variable. (In other words, the callee simply cannot modify the variable, since it lacks a reference to it.)

152. What are enumerations?

They are a list of named integer-valued constants. Example:enum color { black , orange=4,yellow, green, blue, violet };This declaration defines the symbols “black”, “orange”, “yellow”, etc. to have the values “1,” “4,” “5,” … etc. The difference between an enumeration and a macro is that the enum actually declares a type, and therefore can be type checked.

153. Are pointers integer?

No, pointers are not integers. A pointer is an address. It is a positive number.

154. What is static memory allocation?

Compiler allocates memory space for a declared variable. By using the address of operator, the reserved address is obtained and this address is assigned to a pointer variable. This way of assigning pointer value to a pointer variable at compilation time is known as static memory allocation.

155. What is dynamic memory allocation?

A dynamic memory allocation uses functions such as malloc() or calloc() to get memory dynamically. If these functions are used to get memory dynamically and the values returned by these function are assigned to pointer variables, such a way of allocating memory at run time is known as dynamic memory allocation.

156. What modular programming?

If a program is large, it is subdivided into a number of smaller programs that are called modules or subprograms. If a complex problem is solved using more modules, this approach is known as modular programming

157. What is a function?

A large program is subdivided into a number of smaller programs or subprograms. Each subprogram specifies one or more actions to be performed for the larger program. Such sub programs are called functions.

158. Difference between formal argument and actual argument?
Formal arguments are the arguments available in the function definition. They are preceded by their own data type. Actual arguments are available in the function call. These arguments are given as constants or variables or expressions to pass the values to the function.

159. what are C tokens?

There are six classes of tokens: identifier, keywords, constants, string literals, operators and other separators.

160. What are C identifiers?

These are names given to various programming element such as variables, function, arrays.It is a combination of letter, digit and underscore.It should begin with letter. Backspace is not allowed.

161. Difference between syntax vs logical error?

Syntax Error
These involves validation of syntax of language.
compiler prints diagnostic message.

Logical Error
logical error are caused by an incorrect algorithm or by a statement mistyped in such a way that it doesn’t violet syntax of language.
difficult to find.

162. What are the facilities provided by preprocessor?
file inclusion
substitution facility/macro define
conditional compilation

163.What do the functions atoi(), itoa() and gcvt() do?

atoi() is a macro that converts integer to character.
itoa() It converts an integer to string
gcvt() It converts a floating point number to string

164. What is FILE?

FILE is a predefined data type. It is defined in stdio.h file.

 165. What is a file?

A file is a region of storage in hard disks or in auxiliary storage devices.It contains bytes of information .It is not a data type.

166.  What does static variable mean?

There are 3 main uses for the static.

1. If you declare within a function: It retains the value between function calls

2. If it is declared for a function name: By default function is extern..so it will be visible from other files if the function declaration is as static..it is invisible for the outer files 

3. Static for global variables: By default we can use the global variables from outside files If it is static global..that variable is limited to with in the file.

167.  What are the different storage classes in C?

C has three types of storage: automatic, static and allocated.  Variable having block scope and without static specifier have automatic storage duration. 

Variables with block scope, and with static specifier have static scope. Global variables (i.e, file scope) with or without the the static specifier also have static scope.  Memory obtained from calls to malloc(), alloc() or realloc() belongs to allocated storage class.

168.  What is hashing?

To hash means to grind up, and that’s essentially what hashing is all about. The heart of a hashing algorithm is a hash function that takes your nice, neat data and grinds it into some random-looking integer. 

The idea behind hashing is that some data either has no inherent ordering (such as images) or is expensive to compare (such as images). If the data has no inherent ordering, you can’t perform comparison searches. 

169.  Can static variables be declared in a header file?

You can’t declare a static variable without defining it as well (this is because the storage class modifiers static and extern are mutually exclusive). A static variable can be defined in a header file, but this would cause each source file that included the header file to have its own private copy of the variable, which is probably not what was intended.

170.  Can include files be nested?

Yes. Include files can be nested any number of times. As long as you use precautionary measures, you can avoid including the same file twice. In the past, nesting header files was seen as bad programming practice, because it complicates the dependency tracking function of the MAKE program and thus slows down compilation. Many of today’s popular compilers make up for this difficulty by implementing a concept called precompiled headers, in which all headers and associated dependencies are stored in a precompiled state.

 171.  What is a null pointer?

There are 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.

172.  How to reduce a final size of executable?

Size of the final executable can be reduced using dynamic linking for libraries.

173.  Can you tell me how to check whether a linked list is circular?

Create two pointers, and set both to the start of the list. Update each as follows:

while (pointer1) {
pointer1 = pointer1->next;
pointer2 = pointer2->next;
if (pointer2) pointer2=pointer2->next;
if (pointer1 == pointer2) {
print ("circular");
}
}

If a list is circular, at some point pointer2 will wrap around and be either at the item just before pointer1, or the item before that. Either way, its either 1 or 2 jumps until they meet.

174.  Which bit wise operator is suitable for checking whether a particular bit is on or off?

The bitwise AND operator. Here is an example:

enum {
KBit0 = 1,
KBit1,
…
KBit31,
};
if ( some_int & KBit24 )
printf ( “Bit number 24 is ON\n” );
else
printf ( “Bit number 24 is OFF\n” );

175.  Which bit wise operator is suitable for turning off a particular bit in a number?

The bitwise AND operator, again. In the following code snippet, the bit number 24 is reset to zero.

some_int = some_int & ~KBit24;

176.  What is the result of using Option Explicit?

When writing your C program, you can include files in two ways. The first way is to surround the file you want to include with the angled brackets < and >. This method of inclusion tells the preprocessor to look for the file in the predefined default location. This predefined default location is often an INCLUDE environment variable that denotes the path to your include files. 

For instance, given the INCLUDE variable
INCLUDE=C:\COMPILER\INCLUDE;S:\SOURCE\HEADERS; using the #include version of file inclusion, the compiler first checks the C:\COMPILER\INCLUDE directory for the specified file. If the file is not found there, the compiler then checks the  S:\SOURCE\HEADERS directory. If the file is still not found, the preprocessor checks the current directory. 

The second way to include files is to surround the file you want to include with double quotation marks. This method of inclusion tells the preprocessor to look for the file in the current directory first, then look for it in the predefined locations you have set up. Using the #include file version of file inclusion and applying it to the preceding example, the preprocessor first checks the current directory for the specified file. If the file is not found in the current directory, the C:COMPILERINCLUDE directory is searched. If the file is still not found, the preprocessor checks the S:SOURCEHEADERS directory. 

The #include method of file inclusion is often used to include standard headers such as stdio.h or stdlib.h. 

The #include file include nonstandard header files that you have created for use in your program. This is because these headers are often modified in the current directory, and you will want the preprocessor to use your newly modified version of the header rather than the older, unmodified version.