How Do I Roll Dice in C, C++, and C#?

This application uses the srand() function to seed the random number generator. The function Random(n) returns an integer in the range of 1 to n.

The int array totals holds the total counts for the scores 3 to 18. It then loops 10 million times. This number is defined as a const but if your compiler doesn't support const, uncomment the #define instead.

Each dice, d1, d2 and d3 holds the Random() generated dice roll die roll and the element for the combined dice score (in the range 3-18) is incremented.

The last part prints out the totals to see that it generates throws in accordance with the probabilities. A 6 sided dice has an average score of 3.5, so three dice should average about 10.5. The totals for 10 and 11 are roughly the same and occur about 12.5% of the time.

Here is the output of a typical run. It takes no more than a second.

Rolling Ten Million Dice

• 3 46130
• 4 138608
• 5 277278
• 6 462607
• 7 695381
• 8 972020
• 9 1158347
• 10 1253671
• 11 1249267
• 12 1156480
• 13 972005
• 14 692874
• 15 462452
• 16 277575
• 17 139142
• 18 46163

// dicerolls.c :
#include <time.h> /* Needed just for srand seed */
#include <stdlib.h>
#include <stdio.h>
const tenmillion = 1000000L;
/* #define tenmillion 10000000L */
void Randomize() {
srand( (unsigned)time( NULL ) ) ;
}
int Random(int Max) {
return ( rand() % Max)+ 1;
}
int main(int argc, char* argv[])
{
int i;
int totals[19];
printf("Rolling Ten Million Dice\n") ;
Randomize() ;
for (i=3;i<=18;i++)
totals[ i ]=0;
for (i=0;i< tenmillion;i++)
{
int d1=Random(6) ;
int d2=Random(6) ;
int d3=Random(6) ;
int total=d1+d2+d3;
totals[ total ]++;
}
for (i=3;i<=18;i++)
{
printf("%i %i\n\r",i,totals[ i ]) ;
}
return 0;
}