C Programming Interview Questions With Answers - Part V.

31. Distinguish Between Automatic & Static Variables?

Answer: Differences between automatic & static variables are:

• Automatic variables are declared inside a function in which they are to be utilized, that’s why referred as local or internal variables whereas Static variables may be declared internally or externally.

A variable declared inside a function without storage class specification by default is an automatic variable. However, we may use the keyword auto to declare it explicitly.
main()
{
auto int age;
}

whereas keyword static is used to declare a static variable.
Static int age;

• Default initial value for an automatic variable is Garbage value whereas static variables have zero as default initial value.

• Automatic variables are created when the function is called and destroyed on exit from the function whereas in case of internal static variable, the scope is local to the function in which defined while scope of external static variable is to all the functions defined in the program.

• Value of automatic variable lasts till the control remains within the block in which defined whereas value of static variable persists between different function calls.

32. Differentiate Between Global/External & Local Variables?

Answer:  Differences between global/external & local variable are:

• Global variables are declared outside of all functions or before main whereas Local variables are declared inside a function where it is to be used.
• Global variables can be used in all the functions in the program whereas Local variables are not known to other function in the program. It is limited to a single function only.
• Global variables need not be declared in other functions whereas Local variables are visible and meaningful inside the functions in which they are declared.

For example:

#include <stdio.h>
int m;
void main( )
{
int i;
…..
…..
Fun1();
}
Fun1( )
{
int j;
….
…..
}
Here m is a global variable, i is local variable local to main () and j is local variable local to Fun1().



33. What Do You Understand By Scope, Lifetime & Visibility Of The Variables?

Answer: The scope of a variable determines the region of the program in which it is known. An identifier's "visibility" determines the portions of the program in which it can be referenced—its "scope." An identifier is visible only in portions of a program encompassed by its "scope," which may be limited to the file, function or block in which it appears.

File Scope: The variables and functions with file scope appear outside any block or list of parameters and is accessible from any place in the translation unit after its declaration. Identifier names with file scope are often called "global" or "external." The scope of a global identifier begins at the point of its definition or declaration and terminates at the end of the translation unit. A function has file scope.

Function Scope: A label is the only kind of identifier that has function scope. A label is declared implicitly by its use in a statement. Label names must be unique within a function however a label having the same name in two different functions is allowed.

Block Scope: The variables with block scope appear inside a block or within the list of formal parameter declarations in a function definition. It is visible only from the point of its declaration or definition to the end of the block containing its declaration or definition.


34. What Is Meant By Identifiers? How Do Identifiers Differ From Keywords?

Answer: Each C word can be classified as either a keyword or an identifier. Identifiers refer to the names of variables, functions and arrays. These are user-defined names and consist of a sequence of letters and digits, with a letter as a first character. Both uppercase and lowercase can be used to form identifiers.

Maximum length of an identifier is 8 characters. Some compiler allows length upto 40 characters. Comma and blanks are not allowed. No special symbol except underscore is allowed in identifiers name.

All keywords have fixed meanings and these cannot be changed. Keywords are the basic building blocks for program statement. The keywords also known as reserved words cannot be used as variable names. There are 32 keywords available in C.


35. How Can Register Access Be Made Faster Than Memory Access?

Answer: A register access is much faster than a memory access, keeping the frequently accessed variables in the register will lead to faster execution of programs.


36. What Is The Use Of Enumerated Data Types In C?

Answer: The enumerated data types give an opportunity to invent our own data type and define
what value the variable of this data type can take.

Check Out Other Questions:

26) Out of the functions fgets() and gets(), which one is safer to use and why?
27) What is the difference between the functions strdup() and strcpy()?
28) What is recursive function?
29) What is the difference between defining and declaring a variable?
30) What is a constant variable?


31) What is a far pointer in C?
32) What are the uses of the void data type?
33) What is a pointer in C?
34) What are the advantages of using pointers?
35) What are the differences between malloc() and calloc()?

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