/*** bsqrt.c  --- sample program by tsaiwn@cs.nctu.edu.tw
 * ½m²ß: ²©ö¿é¤J + ²©ö¿é¥X + ¨Ï¥Î Library µ{¦¡®w + ²©ö while Loop
 * Description: ¼g­Óµ{¦¡, Ū¤J x, ¦L¥X®Ú¸¹ x  (¥i¥H¥Î Library function)
 * Note: ­n¤@ª½°µ¨ì ¿é¤J­t¼Æ(¨Ò¦p¿é¤J -1 ) ¤~°±¤î!  °O±o­n¦L¥X  Bye bye! 
*** *** ¬Ý¤£À´¥iÁ|¤â½Ð§U±Ð¹L¥h¸ÑÄÀµ¹§AÅ¥ *** ***/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
double x;  //  (ª`·N 1) ÅÜ¼Æ variable;  // C++ ¦¡ªºµù¸Ñ comment
double getDBL(void);   // ¼g¦¨ function ¤ñ¸û¦³¼u©Ê:-)
int main( ) {   // 
     for( ; ; ) {   // Loop forever
         printf("Give me x: ");
         x = getDBL( );   // ¼g¦¨¨ç¼Æ (function; ¨ç¦¡) ¬O­Ó«Ü¦nªº²ßºD
         if( x < 0 ) break;    //   (ª`·N 3) ¥i¥H§ï¥Î§Oªº¤èªk
         printf(" sqrt ®Ú¸¹ %f =%f\n ", x,   sqrt(x) );
          //  
     } // while  
     printf("Bye bye!\n");
     return  0;    //   §iª¾§@·~¨t²Î(OS)ªí¥Ü§Ú­Ì³o¥Dµ{¦¡¥¿±`µ²§ô
 }
double getDBL( ) {  // ¥H«á­n§ï¿é¤J¤èªk¥u­n§ï³o function ´N¥i :-)
    static char buf[999];
    double ans;
    gets(buf);    // NOT safe!
    ans = atof(buf);    // required <stdlib.h>
    return ans;
}
/*** Run on Windows/XP cmd windows
C:\testc>gcc bsqrt.c

C:\testc>a.exe
Give me x: 2
 sqrt ®Ú¸¹ 2.000000 =1.414214
 Give me x: 4
 sqrt ®Ú¸¹ 4.000000 =2.000000
 Give me x: 3
 sqrt ®Ú¸¹ùâ 3.000000 =1.732051
 Give me x: 400
 sqrt ®Ú¸¹ 400.000000 =20.000000
 Give me x: -1
Bye bye!

*****************************/
/*** Run on Unix system (FreeBSD)
3:33pm ccbsd2:LAB-01/> gcc bsqrt.c
/var/tmp//cc7d8uuS.o(.text+0xab): In function `getDBL':
: warning: warning: this program uses gets(), which is unsafe.
/var/tmp//cc7d8uuS.o(.text+0x5b): In function `main':
: undefined reference to `sqrt'
3:33pm ccbsd2:LAB-01/> ./a.out
./a.out: Command not found.
3:33pm ccbsd2:LAB-01/> gcc bsqrt.c -lm
/var/tmp//ccgOfzt7.o(.text+0xab): In function `getDBL':
: warning: warning: this program uses gets(), which is unsafe.
3:33pm ccbsd2:LAB-01/> ./a.out
warning: this program uses gets(), which is unsafe.
Give me x: 3
 sqrt ®Ú¸¹ 3.000000 =1.732051
 Give me x: 2
 sqrt ®Ú¸¹ 2.000000 =1.414214
 Give me x: -1
Bye bye!
3:33pm ccbsd2:LAB-01/>
***===================***/