C / Find 190！ c编程中的（阶乘）

我试着找190! 在C

我将我的变量定义为long double，但我看到它（仅正确）计算到172！：

在那之后，我得到了#INF00000 ……`

有办法吗？

实际上只需几行代码就可以实现bigint实现以计算因子。这是打印前200个阶乘的代码。

 #include  int mult(int n, size_t size, unsigned char *data) { int carry = 0; for (int i = 0; i < size; i++) { int result = data[i] * n + carry; data[i] = result % 100; carry = (result - data[i]) / 100; } return carry != 0; } void print(size_t size, unsigned char *data) { int first = 1; for (int i = 0; i < size; i++) { int d = data[size - i - 1]; if (first && d == 0) continue; printf("%0*d", first && d < 10 ? 1 : 2, d); first = 0; } } int main(int argc, char*argv[]) { for (int fact = 1; fact <= 200; fact++) { unsigned char data[1000] = {1}; for (int i = 1; i <= fact; i++) { if (mult(i, sizeof(data), data)) { return 1; } } printf("%d! = ", fact); print(sizeof(data), data); printf("\n"); } return 0; }

190的因子是：

9680322675255249156123346514615331205418161260462873360750859919944104623425228207640470674933540169424682360525991982916161596983449594045525553704253602287443197783274656957056546338783001340434094795097553229620273057440272298773179365935914105128629426348958748638226084106818484328004851174161755668480000000000000000000000000000000000000000000000

或者，1170位。所以这不适合任何内置类型。你真的需要一个bigint库来表示这么大的东西。

一种方法是使用任意精度算术。您可以自己实现它，也可以使用其中一个库。

注意，即使值为172！你得到的很可能只是近似正确。

此示例（Win32 / Visual Studio Express）程序显示错误变为带有无符号64位的！23：

 #include  #include  unsigned __int64 fact( unsigned __int64 in) { if( in == 1 ) { return 1; } unsigned __int64 f = fact(in-1); printf( "!%3I64u = %20I64u = 0x%016I64X\n", in-1, f, f ); return in*f; } int main( int argc, char * argv[] ) { unsigned __int64 in = atoi(argv[1]); unsigned __int64 f = fact(in); printf( "!%3I64u = %20I64u = 0x%016I64X\n", in, f, f ); return 0; }

跑：

 C:\> Factorial 23 ! 1 = 1 = 0x0000000000000001 ! 2 = 2 = 0x0000000000000002 ! 3 = 6 = 0x0000000000000006 ! 4 = 24 = 0x0000000000000018 ! 5 = 120 = 0x0000000000000078 ! 6 = 720 = 0x00000000000002D0 ! 7 = 5040 = 0x00000000000013B0 ! 8 = 40320 = 0x0000000000009D80 ! 9 = 362880 = 0x0000000000058980 ! 10 = 3628800 = 0x0000000000375F00 ! 11 = 39916800 = 0x0000000002611500 ! 12 = 479001600 = 0x000000001C8CFC00 ! 13 = 6227020800 = 0x000000017328CC00 ! 14 = 87178291200 = 0x000000144C3B2800 ! 15 = 1307674368000 = 0x0000013077775800 ! 16 = 20922789888000 = 0x0000130777758000 ! 17 = 355687428096000 = 0x0001437EEECD8000 ! 18 = 6402373705728000 = 0x0016BEECCA730000 ! 19 = 121645100408832000 = 0x01B02B9306890000 ! 20 = 2432902008176640000 = 0x21C3677C82B40000 ! 21 = 14197454024290336768 = 0xC5077D36B8C40000 ! 22 = 17196083355034583040 = 0xEEA4C2B3E0D80000 ! 23 = 8128291617894825984 = 0x70CD7E2933680000

！21和之后是错误的。