Prepocessor directive

1. Unit-IV
PREPROCESSOR DIRECTIVES

2. INTRODUCTION
 C program execution steps are as
follows:
 (i) the C program is written in
editor, and then
 (ii) compilation,
 (iii) linking and
 (iv) the executable code
generation are to be done.
 In between these stages, there also
involves one more stage i.e.
preprocessor.
 The preprocessor is a program that
processes the source program, before it
is passed to the compiler.

3. INTRODUCTION (cont..)

4. INTRODUCTION (cont..)
 The program typed in the editor is the source code to the
preprocessor.
 The preprocessor then passes the source code to the compiler.
 It is not necessary to write the program with the preprocessor
facility.
 But preprocessor can reduce the execution time of a program,
because it takes place of a function call.

5. INTRODUCTION (cont..)
 One of the most important features of the C language is to offer
preprocessor directives.
 The preprocessor directives are always preferably initialized at the
beginning of the program before the main().
 It begins with a symbol #(hash).
 It can be placed anywhere but quite often, it is declared at the
beginning before the main() function or any particular function.

6. THE #DEFINE DIRECTIVE
 The syntax of the #define directive is as follows:
#define identifier substitute
OR
#define identifier(argument 1… argument N) substitute

7. THE #DEFINE DIRECTIVE (cont..)
Example:
#define PI 3.14
 This statement defines PI as macro templates and 3.14 as macro
substitute.
 During preprocessing, the preprocessor replaces every occurrence
of PI (identifier) with 3.14 (substitute value).
 Here, PI is a macro template and 3.14 is its macro expansion.

8. THE #DEFINE DIRECTIVE (cont..)
 The macro templates are generally declared with capital letters for
quick identification.
 One can also define macros with small letters.
 The macro templates and its expansions must be separated with at
least one blank space.
 It is not necessary to provide space between # and define.

9. THE #DEFINE DIRECTIVE (cont..)
 The macro definition should not be terminated with a semi-colon.
 The words followed by # are not keywords.
 The programmer can use these words for variable names.

10. Use the identifier for 3.14 as PI and write a program to find the area
of circle using it.
# define PI 3.14
void main()
{
float r,area;
clrscr();
printf(“n Enter radius of the circle in cm :-”);
scanf(“%f”,&r);
area=PI*r*r;
printf(“Area of the Circle = %.2f cm^2”,area);
getche();
}

11. Example
Write a program to define and create identifier for C statements and
variables.
1. Read N as 10
2. Replace clrscr() with cls
3. Replace getche() with wait()
4. Replace printf with display

12. Example (cont..)
# define N 10
# define cls clrscr()
# define wait() getche()
# define display printf
void main()
{
int k;
cls;
for(k=1;k<=N;k++)
display(“ %d”,k);
wait();
}
OUTPUT:
1 2 3 4 5 6 7 8 9 10

13. Write a program to define macros for logical operators.
# define and &&
# define equal ==
# define larger >
void main()
{
int a,b,c;
clrscr();
printf(“Enter Three Numbers. :”);
scanf(“%d %d %d”,&a,&b,&c);
if(a larger b and a larger c)
printf(“%d is larger than other two numbers.”,a);
else
if(b larger a and b larger c)
printf(“%d is larger than other two numbers.”,b);
else
if(c larger a and c larger b)
printf(“%d is the larger than other two numbers.”,c);

14. Cont..
else
if(a equal b and b equal c)
printf(“n Numbers are same.”);
}
Output:
 Enter Three Numbers:7 8 4
 8 is larger than other two numbers.

15. Write a program to create identifier for displaying double and triple
of a number.
# define DOUBLE(a) a*2
# define TRIPLE(a) a*3
void main()
{
int a=1;
clrscr();
printf(“nSINGLEtDOUBLEtTRIPLE”);
for(;a<=5;a++)
printf(“n%dt%dt%d”,a,DOUBLE(a),TRI
PLE(a));
getche();
}
SINGLE DOUBLE TRIPLE
1 2 3
2 4 6
3 6 9
4 8 12
5 10 15

16. UNDEFINING A MACRO
 A macro defined with #define directives can be undefined with #undef
directive.
 Syntax:
#undef macro_template substitute
 It is useful, when we do not want to allow the use of macros in any portion
of the program.

17. Write a program to undefine a macro.
# define wait getche()
void main()
{
int k;
# undef wait getche();
clrscr();
for(k=1;k<=5;k++)
printf(“%dt”,k);
wait;
}

18. Cont..
 In the program #undef directive undefines the same macro. Hence,
the compiler
 flags an error message ‘undefined symbol ‘wait’ in function main()’.

19. Write a program to find the largest out of two numbers using macro
with arguments.
# define MAX(x,y) if (x>y) c=x; else c=y;
void main()
{
int x=5,y=8,c;
clrscr();
MAX(x,y);
printf(“n Largest out of two numbers = %d”,c);
getche();
}

20. THE #INCLUDE DIRECTIVE
 The #include directive loads specified file in the current program.
 The macros and functions of loaded file can be called in the current
program.
 The included file also gets complied with the current program.
 The syntax is as given below:
# include “filename”
# include <filename>

21. Cont..
Examples:
 # include “stdio.h”
 # include <stdio.h>
 # include <alloc.h>

22. Write a program to show the use of #include directive:
Make two separate .c files as given below.
Main Program:-
#include <stdio.h>
#include "arith.c"
void main()
{
clrscr();
printf("sum(10, 20) = %dn", sum(10, 20));
getch();
}
arith.c file :-
int sum (int x, int y)
{
return (x + y);
}

23. Cont..
 Output:-
sum(10, 20) =30
Even if sum function is not defined in main program we get result because we
have use #include directive to use sum function defined in “arith.c” file.

24. THE #LINE DIRECTIVE
 In order to renumbering the source text this directive is used. The syntax of
line directive is as follows:
#line <constant> [ <identifier> ]
 This causes the compiler to renumber the line number of the next source
line as given by <constant> and <identifier> gives the current input file.

25. Write a program to demonstrate #line directive (Run this program
by changing #line 15 statement with #line 20 or any other number
and understand the change in output.)
#include<stdio.h>
#include<conio.h>
#line 15
void main()
{
clrscr();
printf("ACPn");
printf("Line Number %dn",__LINE__);
printf("2nd Sem");
getch();
}
 OUTPUT:
ACP
Line Number 19
2nd Sem
Line number is printed 19 because line
following the statement “#line 15” which
is “void main() “ will be renumbered as
line number 15 so the statement
“printf("Line Number %dn",__LINE__);” is
in Line number 19

26. THE PREDEFINED MACROS IN ANSI AND TURBO-C
Predefined Macros Function
_ _DATE_ _ Displays system date in string format.
_ _TIME_ _ Displays system time in string format.
_ _LINE_ _ Displays line number as an integer.
_ _FILE_ _ Displays current file name in string format.

27. Write a program to use predefined macros of ANSI
C/TURBO C.
void main()
{
clrscr();
printf(“nDATE: %s”,_ _DATE_ _);
printf(“nTIME: %s”,_ _TIME_ _);
printf(“nFILE NAME : %s”,_ _FILE_ _);
printf(“nLINE NO. : %d”,_ _LINE_ _);
}
 DATE : March 11 2020
 TIME : 21:07:39
 FILE NAME : PRE_MA~1.C
 LINE NO. : 8

28. STANDARD I/O PREDEFINED STREAMS
(Macros) IN STDIO.H
 The predefined streams automatically open when the program is started.
Macros Function Definition in stdio.h
stdin Standard input device. #define stdin (&_streams[0])
stdout Standard output device. #define stdout (&_streams[1])
stderr Standard error output device. #define stderr (&_streams[2])
stdaux Standard auxiliary device. #define stdaux (&_streams[3])
stdprn Standard printer. #define stdprn (&_streams[4])

29. Write a program to enter text and display it using macro
expansions.
void main()
{
char ch[12];
int i;
clrscr();
printf(“Input a Text : ”);
for(i=0;i<11;i++)
ch[i]=getc(&_streams[0]);
printf(“Text Inputted : ”);
for (i=0;i<11;i++)
putc(ch[i],&_streams[1]);
}
Input a Text: Programming
Text Inputted : Programming

30. THE PREDEFINED MARCOS IN CTYPE.H
 The header file ‘ctype.h’ contains a set of macros that check characters.
Macro Returns True Value If
isalpha(d) d is a letter.
isupper(d) d is a capital letter.
islower(d) d is a small letter.
isdigit(d) d is a digit.
isalnum(d) d is a letter or digit.
isxdigit(d) d is a hexadecimal digit.
isspace(d) d is a space.
ispunct(d) d is a punctuation symbol.
isprint(d) d is a printable character.

31. THE PREDEFINED MARCOS IN CTYPE.H
(cont..)
Macro Returns True Value If
isgraph(d) d is printable, but not be a space.
iscntrl(d) d is a control character.
isascii(d) d is an ASCII code.

32. Write a program to identify whether the entered character is a letter
or digit and capital or small using predefined macros.
# include<ctype.h>
void main()
{
char d;
int f;
clrscr();
printf(“n Enter any character : ”);
d=getche();
f=isalpha(d);
if(f!=0)
{
printf(“n%c is a letter in”,d);
f=isupper(d);
if (f!=0)
printf(“ Capital case”);
else
printf(“ Small Case”);
}
else
{
f=isdigit(d);
if(f!=0)
printf(“n %c is a digit”,d);

33. Cont..
else
{
f=ispunct(d);
if(f!=0)
printf(“n %c is a punctuation symbol”,d);
}
}
getche();
}
Enter any character : C
C is a letter in Capital case