I need random number in C ...

purpleburple · 10-27-2002, 10:49 PM

Hi. As a programming practice I am going to be making a simple text based game similiar to dungeons and dragons. I will need random numbers for damage from attacks, etc. Will using >

result = 1 + rand() % 20

give me a good result for say a number from 1-20?

Or is there a better way to get a random number then using rand()?

I will be programming in C ...

thanks

sarin · 10-28-2002, 02:20 AM

I found this from man page of rand

In Numerical Recipes in C: The Art of Scientific Computing
(William H. Press, Brian P. Flannery, Saul A. Teukolsky,
William T. Vetterling; New York: Cambridge University
Press, 1992 (2nd ed., p. 277)), the following comments are
made:
"If you want to generate a random integer between 1
and 10, you should always do it by using high-order
bits, as in

j=1+(int) (10.0*rand()/(RAND_MAX+1.0));

and never by anything resembling

j=1+(rand() % 10);

(which uses lower-order bits)."

Hope this helps.
--Sarin

GtkUser · 10-28-2002, 02:22 AM

Code:

#include<stdio.h>

int main()
{
  int ix;
  srand(); //seed for random number generator

  for ( ix = 0; ix < 50; ++ix)
    printf("%d\n", rand() % 20 + 1);

  return 0;
}

I tested this and it worked, but there are better algorithms. This is the basic way to get a random number using the standard C library. Read the Link page for more information.
< http://www.mkssoftware.com/docs/man3/srand.3.asp >

purpleburple · 10-28-2002, 03:02 AM

thanks guys

gluon · 10-28-2002, 04:37 AM

Hi purpleburple,

Try this :

double MRG32k3a () /* P. L'Ecuyer 's generator*/
{
long k;
double p1, p2;
/* Component 1 */
p1 = a12 * s11 - a13n * s10;
k = p1 / m1; p1 -= k * m1; if (p1 < 0.0) p1 += m1;
s10 = s11; s11 = s12; s12 = p1;
/* Component 2 */
p2 = a21 * s22 - a23n * s20;
k = p2 / m2; p2 -= k * m2; if (p2 < 0.0) p2 += m2;
s20 = s21; s21 = s22; s22 = p2;
/* Combination */
if (p1 <= p2) return ((p1 - p2 + m1) * norm);
else return ((p1 - p2) * norm);
}

It's one of the best random number generator

Hope it helps, CU

gluon