What is algorithm to calculate the factorial of an user given number?

Answer 1

Note: The recursive portions of this code can use a lot of stack space. You may need to tell your linker to allocate more space to prevent a stack overflow exception.

To calculate the factorial of a user given number, simply multiply all of the integers between 2 and that number, inclusive, together. There are two fundamental algorithms; iterative and recursive...

Iterative uses a loop of some sort to iterate through each multiplier and multiply that to the running product.

These examples were developed and checked on the Microsoft Windows SDK 7. Portable compilers might not like the 64-bit long long data type.

/* Microsoft 32-bit iterative */

unsigned long NFactLongIterative (unsigned long N) {

unsigned long result = N;

if (N < 2) return 1;

if (N 2) {

decimal_initialize (d, 2);

return;

}

while (N > 2) {

decimal_multiply (d, N);

N--;

}

return;

}

Main line code, showing full functionality

#include

... all of the above routines are inserted here

/* Example main line */

/* Generates all variations to show differences in results */

int main (int argc, char *argv[]) {

int N;

decimal Decimal = {2, NULL};

if (argc < 2) {

fprintf (stderr, "Usage: factorial N\n");

return 1;

}

N = atoi (argv[1]);

printf ("Long: %u! = %u\n", N, NFactLongIterative (N));

printf ("LongLong: %u! = %I64u\n", N, NFactLongLongIterative (N));

printf ("Recursive: %u! = %I64u\n", N, NFactLongLongRecursive (N));

printf ("Double: %u! = %.0f\n", N, NFactDouble (N));

/* note: arbitrary is exact - if the others don't match, arithmetic overflow occurred */

printf ("Arbitrary: %u! = ", N);

decimal_NFactIterative (&Decimal, N);

decimal_print_digits (&Decimal, TRUE);

return 0;

}