Question

Question 2.

  Explain preprocessor directives in C.

1. Describe Error and pragma directives and write code snippets.
2. Describe define, and undef, directives.
3. Write the code which shows if constant “VALUE” is not defined then define it and replace its value to 5 on runtime. Display the value of x.

int x = VALUE;

Answer 1

1)Preprocessor Directives:These begin with # symbol.These directives normally used to include the header files such as stdio.h,stdlib.h,math.h,string.h

eg:#include<stdio.h>

#include<math.h>

2)#error directive will print an implementation-dependent message including the tokens specified in the directive.

#pragma directive tokens are a series of characters that gives a specific compiler instruction and arguments,if any and causes an implementation-defined action.

3)#define directive specifies a macro identifier and a replacement list,and terminates with a new line character.

#undef directive cancels a previous definition of the identifier by #define.