//Adapted from this answer: https://stackoverflow.com/a/44053522/920069
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
char* factorial(int input1)
{
	int val[200] = { 0 }; //100! is 158 digits
	int carry = 0;
	int size = 0;
	val[size++] = 1;
	for (int i = 2; i <= input1; i++)
	{
		for (int j = 0; j < size; j++)
		{
			int tmp = val[j] * i;
			val[j] = (tmp + carry) % 10;
			carry = (tmp + carry) / 10;
		}
		while (carry != 0)
		{
			val[size++] = carry % 10;
			carry = carry / 10;
		}
	}
 
	char* ret = calloc(size+1, 1);
	for (int i = 0; i < size; ++i)
	{
		ret[i] = val[size - i - 1] + '0';
	}
	return ret;
}
 
int main(void)
{
	char* f = factorial(100);
	printf("%s\n", f);
	return 0;
}
 

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