[2016-06-13] Challenge #271 [Easy] Critical Hit

critical.c

#include <stdio.h>
#include <cs50.h>
#include <math.h>

/* [2016-06-13] Challenge #271 [Easy] Critical Hit
 * http://bit.ly/1sLH0bn
 * 
 * Critical hits work a bit differently in this RPG. If you roll the maximum value on a die, you
 * get to roll the die again and add both dice rolls to get your final score. Critical hits can
 * stack indefinitely -- a second max value means you get a third roll, and so on. With enough
 * luck, any number of points is possible.
 *
 */

double p = 0;

// probability of a favorable outcome
double probability(double d, double h)
{
  	if (d < h)
  	{
  		return ((1/d) * probability(d,(h-d))); // recursive case.
  	}
  	if (d >= h)
  	{
  		return ((d-h)+1)/d; // base case of a favorable outcome in the number of sides is >= hp left
  	}
  	return 0;
}

int main(void) {
	// Disable stdout buffering
    	setvbuf(stdout, NULL, _IONBF, 0);
	
	// Put the die numbers and hp numbers into arrays
	int arrd[] = {4,4,4,4,1,100,8};
	int arrh[] = {1,4,5,6,10,200,20};
	
	// Need to loop through arrays to be able to print out the outputs
	for (int i = 0; i < 7; i++)
	{
		// d and h just look better to me than using the arrd and arrh
		double d = arrd[i];
		double h = arrh[i];
	    
		p = probability(d,h);
	    	printf("d = %i, h = %i, output = %.9f\n", arrd[i], arrh[i], p); //print to 9 decimal places
	}
}

output.txt

d = 4, h = 1, output = 1.000000000
d = 4, h = 4, output = 0.250000000
d = 4, h = 5, output = 0.250000000
d = 4, h = 6, output = 0.187500000
d = 1, h = 10, output = 1.000000000
d = 100, h = 200, output = 0.000100000
d = 8, h = 20, output = 0.009765625

My solution to this coding problem on reddit: https://www.reddit.com/r/dailyprogrammer/comments/4nvrnx/20160613_challenge_271_easy_critical_hit/

I am using CS50's library as that is the only programming class I'm taking at the moment and am only on week 4. I am sure there is a way to simplify the probability formula as well.

Biggest hurdle was thinking about what the recursive case and base case would be. The twist is that there is always a chance if you roll the largest number on the die so (1/d) * (the next probability) and so on and so forth.

I am not so good with understanding how to use the data types so I chose double for everything since a lot of division was involved. Also I don't know a good way to format the output. I don't know how to put it into a nice grid or anything like that.

Also I should be dealing with memory allocation and clearing, but I only just learned how in CS50 and haven't implemented it over there yet.