Question based on C language..

1) What are the key features of C programming language?

·         C is a platform-dependent language.

·         C offers the possibility to break down a large program into small modules.

·         Also, the possibility of a programmer to control the language.

·         C comes with support for system programming and hence it compiles and executes with high speed when compared to other high-level languages.

2) What is the use of header files in C?

Header files contain the definitions and set of rules of the functions being used in the programs.

For example:- 

 when you use printf() or scanf() in your program, you nee to include stdio.h library function. Else your compiler will show an error. This is because, the standard input and output functions printf() and scanf() are stored in this header file.

So similarly every header file stores a set of predefined functions which makes it easy to program.

3) What happens if a headerfile is included twice? 

When the pre-processor sees a #include, it replaces the #include with the contents of the specified header. By using include guard(#), you can prevent a header file from being included multiple times during the compilation process. So basically, if a header file with proper syntax is included twice, the second one gets ignored.

4) Can a program be compiled without the main() function?

Yes, compilation is possible, but the execution is not possible. However, if you use #define, we can execute the program without the need of main().

For Example:

#include<stdio.h>    

#define start main    

void begin() {    

   printf("Hello World");    

}

5) What is the difference between static & global variables?

Global variables are variables which are defined outside the function. The scope of global variables begins at the point where they are defined and lasts till the end of the file/program. Whereas, static global variables are private to the source file where they are defined and do not conflict with other variables in other source files which would have the same name.

6) What is Memory Leak in C?

A memory leak occurs when programmers create a memory in the heap and forget to delete it. It decreases the efficiency of the performance of the system.

7) What is the difference between while (0) and while (1)?

While(1) is an infinite loop which will run till a break statement occurs. Similarly, while(2), while(3), while(255) etc will all give infinite loops only.

Whereas, While(0) does the exact opposite of this. When while(0) is used, it means the conditions will always be false. Thus, as a result, the program will never get executed. 

8) What is a Dangling Pointer in C?

A pointer pointing to a de-referenced memory location is called dangling pointer. i.e. pointer pointing to the memory location which is deleted. There are three different ways where a pointer can act as a dangling pointer.

·         De-allocation of memory

·         When the local variable is not static

·         When the variable goes out of scope

9) What is the difference between the Void and Null Pointer?

Null pointers generally do not point to a valid location.  A pointer is initialized as NULL if we are not aware of its value at the time of declaration. 

Whereas, Void pointers are general-purpose pointers which do not have any type associated with them and can contain the address of any type of variable. So basically, the type of data that it points to can be anything. 

10) Difference between malloc() and calloc() functions?

malloc and calloc are library functions that allocate memory dynamically, which means that memory is allocated during the runtime from the heap segment.

Malloc and Calloc differ in the number of arguments used, their initialization methods and also in the return values

11) What is the difference between a structure and a Union?

·         All the members of a structure can be accessed simultaneously but union can access only one member at a time

·         Altering the value of a member will not affect the other members of the structure but where it affects the members of a union

·         Lesser memory is needed for a union variable than a structure variable of the same type

12) Write a program to print “hello world” without using a semicolon?

#include <stdio.h>      

void main()

{      

 if(printf("Hello World"))

{

}}