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Preprocessor

Preprocessor,
math.h
stdlib.h

Preprocessor
? Preprocessor
�C Permits to define simple macros that are evaluated and
expanded prior to compilation.
�C Commands begin with a ��#��.
�C #define : defines a macro [Ex] #include <stdio.h>
�C #undef : removes a macro definition #define PI 3.14159
�C #include : insert text from file
�C #if : conditional based on value of expression
�C #ifdef : conditional based on whether macro defined
�C #ifndef : conditional based on whether macro is not defined
�C #else : alternative
�C #elif : conditional alternative
�C defined() : preprocessor function: 1 if name defined, else 0
#if defined(__NetBSD__)

2

Preprocessor
? #include <filename> or #include ��filename��
�C Include contents of filename in this position (not modify your
source file, but make a new temporary file just before compile)
�C <> is used if filename is in the system default directory
(Most of the standard header files are in the default directory)
�C �� is used if filename is not in the default directory
(Write the path to filename if it is not in the current directory)

[Ex]
Include stdio.h which is in the default
#include <stdio.h>
directory
#include ��./test/file.h��

Include file.h in test directory.

3

Preprocessor
? Header file
�C Header files with the extension ��.h�� are included by #include

? Contents of Header file
�C Prototype of Function
�C ��extern�� global variables Refer to Modulization
�C type definition, etc.

? Typical header files
�C stdio.h, stdlib.h, math.h, etc.

4

Preprocessor
? #define [identifier] [replacement]
�C replaces any occurrence of identifier in the rest of the code by
replacement.
�C replacement can be an expression, a statement, a block or simply
anything.

[Ex]

#define LIMIT 100 Preprocessor regards LIMIT as 100,
#define PI 3.14159 PI as 3.141592.

5

Preprocessor
? #define
#include <stdio.h>
#define LIMIT 100
#define PI 3.14159
void main(void)
{
printf( ��%d, %fn��, LIMIT, PI ) ;
}
Preprocessor makes a temporary file.

��
After that, compile the temporary file.
void main(void)
{
printf( ��%d, %fn��, 100, 3.14159 ) ;
}

6

Preprocessor
? Example

#include <stdio.h> void main(void)
{
#define YELLOW 0 int color ;
#define RED 1
#define BLUE 2 for( color = YELLOW ; color <= BLUE ; color++ ) {
switch( color ) {
case YELLOW : printf( ��Yellown�� ) ; break ;
case RED : printf( ��Redn�� ) ; break ;
case BLUE : printf( ��Bluen�� ) ; break ;
}
}
}

7

Preprocessor
? Macro function: Declare a function by using #define

#define multiply(a,b) ((a)*(b))

void main() {
int c = multiply(3,2) ;
}

�C Compiled after the code modified by preprocessor as follows.

void main() {
int c = ((3)*(2)) ;
}

8

Preprocessor
? Macro function: Be careful! Simple replacement!!
�C what will happen?

#define multiply(a,b) a*b

void main() {
int c = multiply(3+1,2+2) ;
}

�C Compiled after the code modified by preprocessor as follows.

void main() {
int c = 3+1*2+2 ;
}

�C Use ��()�� for safety.

9

Mathematical Functions

? Mathematical Functions
�C sqrt(), pow(), exp(), log(), sin(), cos(), tan(), etc.
�C Include the Header file <math.h>
�C All the math functions have argument with double type and
return value with double type.

[Ex] double sin(double); /* argument is the angle in radians */
double pow(double, double);

�C Give ��-lm�� flag when you compile this with Unix(gcc).

[Ex] gcc filename.c -lm

11

Mathematical Functions

[Ex] #include <stdio.h>
#include <math.h>

#define PI 3.1415926

int main() {
double r = PI / (2*90); /* 180 radian = 1 degree */
int i;

for(i=0; i<=90; i+=5) {
printf("cos(%d) = %ft", i, cos(r*i));
printf("sin(%d) = %ft", i, sin(r*i));
printf("tan(%d) = %fn", i, tan(r*i));
} cos(0) = 1.000000 sin(0) = 0.000000 tan(0) = 0.000000
} ��
cos(45) = 0.707107 sin(45) = 0.707107 tan(45) = 1.000000
��
cos(90) = 0.000000 sin(90) = 1.000000 tan(90) = 37320539.634355

12

Miscellaneous functions
? Standard Headers you should know about:
�C stdio.h: file and console (also a file) IO
? perror, printf, open, close, read, write, scanf, etc.
�C stdlib.h: common utility functions
? malloc, calloc, strtol, atoi, etc
�C string.h: string and byte manipulation
? strlen, strcpy, strcat, memcpy, memset, etc.
�C math.h: math functions
? ceil, exp, floor, sqrt, etc.

14

? Standard Headers you should know about:
�C ctype.h: character types
? isalnum, isprint, isupport, tolower, etc.
�C errno.h: defines errno used for reporting system errors
�C signal.h: signal handling facility
? raise, signal, etc
�C stdint.h: standard integer
? intN_t, uintN_t, etc
�C time.h: time related facility
? asctime, clock, time_t, etc.

15


? Miscellaneous Functions
�C atoi(), rand(), srand()
�C <stdlib.h>: Common Utility Functions
�C atoi(��String��): Convert string to integer
int a = atoi( ��1234�� ) ;

�C rand() : Generate random number
int a = rand() ;

�C srand( Initial Value ) : Initialize random number generator
srand( 3 ) ;

16


? Ex.: Print 10 random numbers
#include <stdio.h>
#include <stdlib.h>

int main() {
Run this Program twice
for(i=0; i<10; i++)
printf(��%dn��, rand() ) ;
}

? Print different random number in every execution
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main() {
srand( (int)time(NULL) ) ;
for(i=0; i<10; i++)
printf(��%dn��, rand() ) ;
}
17

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3 1. preprocessor, math, stdlib

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