rahuljose:

I am sure there is a simpler mathematical solution but this is good enough for now I have always been a brute force guy sadly

#include<stdio.h>
void main()
{
	int i; 
	long double p=1;
	for(i=1;i<101;i++)
	{
		p=p*i;
	}
	printf("Product of all numbers between 1&100 is %LG \n",p);
}

No Compiler installed no issues head to http://codepad.org/

PS:-

The answer is 152 zeroes.

My takeaway from this is the printf Format placeholder for Long Double-%LG

Actually, there is a better (and more accurate way.

Note that your double isn’t large enough to hold a value as large as 100!, neither is the unsigned long. But Java does have the BigNumber object that can be used to store numbers larger than you can imagine.
[EDIT] I’m not sure about this. I didn’t remember the long double extended-precision format. Assumed it was 64-bits like the double. Rahul pointed out that it was indeed capable of storing values as large enough as 100!

What you’d have to do in C is to keep an array to keep track of all those digits and then perform the computation as if you were writing it down on pen and paper, take each thing one-by-one and multiply. I will work on a possible solution to this.