算100！的C++程序

来源: 怪哉于 2009-02-10 22:54:18 [档案] [博客] [旧帖] [给我悄悄话] 阅读数 : (2034 bytes)

// calculate large factorials (factorials above 12!)
// note that 13! already exceeds unsigned long
// a Dev-C++ tested console program by vegaseat 26mar2005

#include
#include

using namespace std;

int main()
{
unsigned int nd, nz; // number of digits
unsigned char *ca; // char array to hold result
unsigned int j, n, q, temp;
int i;
double p;

while(1)
{
cout cin >> n;

if (n == 0) break;

//calculate nd = the number of digits required
p = 0.0;
// p is really log10(n!)
for(j = 2; j {
p += log10((double)j); // cast to double
}

nd = (int)p + 1;
// allocate memory for the char array
//ca = new unsigned char[nd];
ca = (unsigned char*)malloc(sizeof(unsigned char)*(nd+1));
if (!ca)
{
cout exit(0);
}
//initialize char array
for (i = 1; i {
ca[i] = 0;
}
ca[0] = 1;

// put the result into a numeric string using the array of characters
p = 0.0;
for (j = 2; j {
p += log10((double)j); // cast to double!!!
nz = (int)p + 1; // number of digits to put into ca[]
q = 0; // initialize remainder to be 0
for (i = 0; i {
temp = (ca[i] * j) + q;
q = (temp / 10);
ca[i] = (char)(temp % 10);
}
}

cout // the factorial is stored in reverse, spell it from the back
for( i = nd - 1; i >= 0; i--)
{
cout }
cout
// free up allocated memory
free(ca);
} // while

return 0;
}