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// shamelessly ukradeno iz
// https://www.geeksforgeeks.org/factorial-large-number/
// Maximum number of digits in output
#include <stdio.h>
#include <stdlib.h>
#define MAX 5000
int multiply(int x, int res[], int res_size);
// This function finds factorial of large numbers
// and prints them
void factorial(int n)
{
int res[MAX];
// Initialize result
res[0] = 1;
int res_size = 1;
// Apply simple factorial formula n! = 1 * 2 * 3 * 4...*n
for (int x=2; x<=n; x++)
res_size = multiply(x, res, res_size);
fprintf(stdout, "Factorial of given number is \n");
for (int i=res_size-1; i>=0; i--)
fprintf(stdout, "%d", res[i]);
fprintf(stdout, "\n");
}
// This function multiplies x with the number
// represented by res[].
// res_size is size of res[] or number of digits in the
// number represented by res[]. This function uses simple
// school mathematics for multiplication.
// This function may value of res_size and returns the
// new value of res_size
int multiply(int x, int res[], int res_size)
{
int carry = 0; // Initialize carry
// One by one multiply n with individual digits of res[]
for (int i=0; i<res_size; i++)
{
int prod = res[i] * x + carry;
// Store last digit of 'prod' in res[]
res[i] = prod % 10;
// Put rest in carry
carry = prod/10;
}
// Put carry in res and increase result size
while (carry)
{
res[res_size] = carry%10;
carry = carry/10;
res_size++;
}
return res_size;
}
// Driver program
int main(int argc, char ** argv) {
if(argc != 2) {
fprintf(stderr, "uporaba: %s stevilka\n", argv[0]);
return 1;
}
factorial(atoi(argv[1]));
return 0;
}
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