🔒 Locked

random numbers?

Started by DM7 Jul 30, 2002 at 2:17 AM 4 replies 500+ views

Original Post

Jul 30, 2002 at 2:17 AM

How do I generate random numbers in c++? I also need to know how to have a number vary slightly like hp damage in an RPG

necr0

Jul 30, 2002 at 3:05 AM

rand() ????

if you want the random number within a certaion range 0 to ?

then write a function such as :

  
int Random(int range)
{
	if (range == -1)  // check for divide-by-zero case

	{
		return((rand() % 2) - 1);
	}
		
	return(rand() % (range + 1));
}

if you want the numbers to be within a specified low and high range write a function like :

  
int Random(int lo, int hi)
{
	if ((hi - lo + 1) == 0)		// check for divide-by-zero case

	{
		if (rand() & 1) return(lo);
		else return(hi);
	}

	return((rand() % (hi - lo + 1)) + lo);
}

for floats this would be :

  
float Random(float min, float max)
{
	float randNum = (float)rand() / RAND_MAX;
	float num = min + (max - min) * randNum;
	return num;
}

hth

necr0

[edited by - necr0 on July 30, 2002 4:07:30 AM]

DM7

Jul 30, 2002 at 12:59 PM

hey thanks

are there any header files that I should include to use rand()?
I get an error that rand has an undeclared identifier. Normally I''d know how to fix this but I don''t know what I would put in a rand() function

I''m kinda new to this.. over only covered up to references in c++. So if I say something dumb I hope you''ll forgive me

acraig

Jul 30, 2002 at 1:03 PM

Under linux, rand() is in stdlib.h. I would assume that it is the same under Windows.

-------
Andrew

[edited by - acraig on July 30, 2002 2:05:23 PM]

cgoat

Jul 30, 2002 at 1:52 PM

And don't forget to call srand() once at the beginning of your program, otherwise you'll generate the same random numbers every time you run your program.

  
#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <ctime>


using namespace std;

int main()
{
  srand(time(NULL));

  int i;
  for(i=0; i<1000; ++i)
  {
    int r = rand() % 16;
    cout << "Random Value: " << r << endl;
  }

  return 0;
}

[edited by - cgoat on July 30, 2002 2:53:10 PM]

Stoffel

Jul 30, 2002 at 5:54 PM

Never use modulo (%) with rand. See exhaustive discussion here.

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.