// Recursive 遞迴的好處就是想好了就寫好了, 因為怎模想就怎麼寫 :-)
//fact.c   --- @CopyLeft by tsaiwn@csie.nctu.edu.tw
// C99 認識  long long 用 64 bits 可算到 20 !  但 21! 還是掛掉
#include <stdio.h>
long long fact(int n) {
    if(n == 0) return 1;  // 0! 是 1
    return n * fact( n-1 );  // n階乘就是 n 乘以 n-1 階乘
}
long ha(int n) {   // 用  long 只能算到 12 ! 之後的就掛了
    if(n < 0) return -ha( -n );  // 負的 -n 階乘
    if(n == 0) return 1;  // 0! 是 1
    return n * ha( n-1 );  // n階乘就是 n 乘以 n-1 階乘
}
int main ( ) {
    int i;
#ifdef __TURBOC__
    printf(" ..TC++3.x NOT supports long long.\n");
#endif
    for(i=0; i <= 21; ++i) {
       printf("%2d! = ", i);
#ifdef __MINGW32__
       printf("%I64d", fact(i) );   // DEV-C++ use MINGW32 gcc
#else
       printf("%lld", fact(i) );   // other C/C++ long long 要用 %lld 喔
#endif
       //printf("%I64d", fact(i) );  // 注意 DEV C++ 用 %I64d 
       printf("\n");
    }
    for(i=0; i <= 18; ++i) 
       printf("ha(%2d)= %ld\n", i, ha(i)); // 注意是 Long
    return 0;
}
/***********
 0! = 1
 1! = 1
 2! = 2
 3! = 6
 4! = 24
 5! = 120
 6! = 720
 7! = 5040
 8! = 40320
 9! = 362880
10! = 3628800
11! = 39916800
12! = 479001600
13! = 6227020800
14! = 87178291200
15! = 1307674368000
16! = 20922789888000
17! = 355687428096000
18! = 6402373705728000
19! = 121645100408832000
20! = 2432902008176640000
21! = -4249290049419214848
ha( 0)= 1
ha( 1)= 1
ha( 2)= 2
ha( 3)= 6
ha( 4)= 24
ha( 5)= 120
ha( 6)= 720
ha( 7)= 5040
ha( 8)= 40320
ha( 9)= 362880
ha(10)= 3628800
ha(11)= 39916800
ha(12)= 479001600
ha(13)= 1932053504
ha(14)= 1278945280
ha(15)= 2004310016
ha(16)= 2004189184
ha(17)= -288522240
ha(18)= -898433024
************************//////