3 1. preprocessor, math, stdlib

3 1. preprocessor, math, stdlib

• 1.
  Preprocessor Preprocessor, math.h stdlib.h
• 2.
  Preprocessor  Preprocessor – Permits to define simple macros that are evaluated and expanded prior to compilation. – Commands begin with a ‘#’. – #define : defines a macro [Ex] #include <stdio.h> – #undef : removes a macro definition #define PI 3.14159 – #include : insert text from file – #if : conditional based on value of expression – #ifdef : conditional based on whether macro defined – #ifndef : conditional based on whether macro is not defined – #else : alternative – #elif : conditional alternative – defined() : preprocessor function: 1 if name defined, else 0 #if defined(__NetBSD__) 2
• 3.
  Preprocessor  #include <filename>or #include “filename” – Include contents of filename in this position (not modify your source file, but make a new temporary file just before compile) – <> is used if filename is in the system default directory (Most of the standard header files are in the default directory) – “” 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
• 4.
  Preprocessor  Header file – Header files with the extension “.h” are included by #include  Contents of Header file – Prototype of Function – ‘extern’ global variables Refer to Modulization – type definition, etc.  Typical header files – stdio.h, stdlib.h, math.h, etc. 4
• 5.
  Preprocessor  #define [identifier][replacement] – replaces any occurrence of identifier in the rest of the code by replacement. – 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
• 6.
  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
• 7.
  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
• 8.
  Preprocessor  Macro function:Declare a function by using #define #define multiply(a,b) ((a)*(b)) void main() { int c = multiply(3,2) ; } – Compiled after the code modified by preprocessor as follows. void main() { int c = ((3)*(2)) ; } 8
• 9.
  Preprocessor  Macro function:Be careful! Simple replacement!! – what will happen? #define multiply(a,b) a*b void main() { int c = multiply(3+1,2+2) ; } – Compiled after the code modified by preprocessor as follows. void main() { int c = 3+1*2+2 ; } – Use ‘()’ for safety. 9
• 10.
  Math functions (math.h)
• 11.
  Mathematical Functions  MathematicalFunctions – sqrt(), pow(), exp(), log(), sin(), cos(), tan(), etc. – Include the Header file <math.h> – 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); – Give “-lm” flag when you compile this with Unix(gcc). [Ex] gcc filename.c -lm 11
• 12.
  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
• 13.
  Misc. functions (stdlib.h)
• 14.
  Miscellaneous functions  StandardHeaders you should know about: – stdio.h: file and console (also a file) IO • perror, printf, open, close, read, write, scanf, etc. – stdlib.h: common utility functions • malloc, calloc, strtol, atoi, etc – string.h: string and byte manipulation • strlen, strcpy, strcat, memcpy, memset, etc. – math.h: math functions • ceil, exp, floor, sqrt, etc. 14
• 15.
  Miscellaneous functions  StandardHeaders you should know about: – ctype.h: character types • isalnum, isprint, isupport, tolower, etc. – errno.h: defines errno used for reporting system errors – signal.h: signal handling facility • raise, signal, etc – stdint.h: standard integer • intN_t, uintN_t, etc – time.h: time related facility • asctime, clock, time_t, etc. 15
• 16.
  Miscellaneous functions  MiscellaneousFunctions – atoi(), rand(), srand() – <stdlib.h>: Common Utility Functions – atoi(“String”): Convert string to integer int a = atoi( “1234” ) ; – rand() : Generate random number int a = rand() ; – srand( Initial Value ) : Initialize random number generator srand( 3 ) ; 16
• 17.
  Miscellaneous functions  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