[CoLoCo] dice rolls in C

[Kevin Fries]

Hopefully my comments will help you understand.  Changing from 3 dice to
two is pretty trivial.  Ask again if this explanation does not help you
figure it out on your own.

Kevin


#include <time.h> /* Needed just for srand seed */
#include <stdlib.h>
#include <stdio.h>

>> These are optional libraries and headers.  Stdlib is included
>> in most programs, and stdio is included whenever you are outputing
>> direct from the program (i.e. no x)

const tenmillion = 1000000L;
 /* #define tenmillion 10000000L */

>> This simply defines a constant value to use instead of a number

 void Randomize() {
   srand( (unsigned)time( NULL ) ) ;
 }

>> This function calls the random number generator with the current time
>> in milliseconds as a seed to further randomize the value.  The value
>> returned will be between 0 and 1.

 int Random(int Max) {
   return ( rand() % Max)+ 1; 
 }

>> This calls the last function and converts it to a number between 0 
>> and 1 to a number between 1 and Max.

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

>> This is just a counter variable being declared for future use

  int totals[19];

>> This will hold a counter of how many times the three rolls total
>> a certain value.  Three dice x six sides = 18 values, not sure why
>> they made it 19.  Think about it, 0, 1, and 2 are also impossible 
>> values, so this could have been 15 since their are only 15 possible
>> values, but he made it 18 (19?) to make logic easier later.

  printf("Rolling Ten Million Dice\n") ;
  Randomize() ;

>> seed the random number generator

for (i=3;i<=18;i++)
  totals[ i ]=0;

>> Make sure all legal values (3-18) start from zero

for (i=0;i< tenmillion;i++) {

>> loop 10 Million times

  int d1=Random(6) ;
  int d2=Random(6) ;
  int d3=Random(6) ;

>> Get a random number from 1 to 6 for each of three die d1, d2, d3

  int total=d1+d2+d3;

>> Get the total amount of the roll

  totals[ total ]++;

>> Add 1 to the total counter.  i.e. if you rolled 6, 3, 2 the total
>> will equal 11, so add one to total number 11.  This creates what is
>> known as a histogram.
}

for (i=3;i<=18;i++) {
  printf("%i %i\n\r",i,totals[ i ]) ;
}

>> Print the results in the form of "# total" for all legal values
>> (3-18)

  return 0;

>> all functions in C return an integer value by default, so return
>> 0.  Since this is the controlling function, the 0 will be returned
>> to the OS as the errorlevel.  With error checking, you could have
>> returned a 1 on error, and checked this value in your bash script.
}

On Tue, 2008-02-05 at 09:08 -0700, Jim Hutchinson wrote:
> In my attempts to learn about RNGs and programming tools, I stumbled
> upon a little program apparently written in C. How do I compile or run
> this in Ubuntu? Anyone know how to change it from 3 dice to 2? It's
> mostly gibberish to me.
> 
> http://cplus.about.com/od/thecden/a/dicerolls.htm
> 
> Thanks,
> Jim
> 
> -- 
> Please avoid sending me Word or PowerPoint attachments.
> See http://www.gnu.org/philosophy/no-word-attachments.html
> 
-- 
Kevin Fries
Senior Linux Engineer
Computer and Communications Technology, Inc
A Division of Japan Communications Inc.