Dev C++ random number generator

[Mathew Thomas]

Hey guys,

I am darkshade and I am new to programming in C++.

At the moment I have to create a project which will play the traditional tic-tac-toe game.

I got the proram to do the design for me. now its just that I am planning ot generate a random number between 0 and 8 so that when the user click a button, it will generate a number and will put a cross on that panel

BTW, I have 9 panels on which the cross and noughts appear.

But my random number generator generates the same random numbers and I get the cross on top of an already obtained panel.

Please help me out.

D

[Mathew Thomas]

OK but still I need to generate 9 random numbers which are unique (i.e) they dont repeat again. But your link helps a lot. Thanks man.

Ill let u guys know how Im doing.

Thanks for all your advice and help.

[cpns]

I guess you did not get my point; they are not random numbers! They are a clearly defined set of numbers (0..8) in a random order.

Start with an array:

int chk_array[] = {0,1,2,3,4,5,6,7,8} ;

Then apply the Knuth shuffle algorithm on that array.

If you want to see how bad a shuffle can be if you do not apply sound statistical theory, take a look at this: http://www.codinghorror.com/blog/archives/001015.html

Clifford

[Anonymous]

Try call srand() before calling rand()

That start a new sequence of pseudo-random integers to be returned by rand().

See the manual for details.

HTH

[Kurgusov]

heres the RNG I use as a function.

include <ctime>

include <cstdlib>

int roll (int high, int low)
{
int range = high - low +1 ;
int val = (rand() % range) + low ;
return val ;
}

now you have your rn generator you get a random seed from the computer clock,
e.g.

int main (int argv, int* argc [])
{
int seed = time (NULL) ;
srand (seed) ;

//those two lines sets up the value of seed.
//you only need to do this once for the duration of your program btw

//then test your RNG

for (int i=0; i<100; i++){
std::cout << roll (100, 1) << " : " ;
}

system ("pause") ;
return 0 ;

}

have fun!

[Mathew Thomas]

hey I have a small idea of how to do it. I dont know If Im going the long way. but here it is. As I told u before, Im creating a Graphical Tic-tac toe game.

Im testing whether it will work on a normal console application. if it works then I can implement it into my main program. here is the code which I have right now.

include <stdio.h>

include <conio.h>

include <stdlib.h>

include <time.h>

int main (void)
{
int a, test, chk_array[9], chk_no, chk_dec = 9;
srand(time(NULL));

for(chk_no = 0; chk_no < 9; ++chk_no)
{
 chk_array[chk_no] = rand () % chk_dec;
}

for(chk_no = 0; chk_no < 9; ++chk_no)
{
  printf ("chk_array [%d] [%d] \n", chk_no, chk_array[chk_no]);
}

system("PAUSE");
return 0;

}

Now this code generates different random numbers every time it runs from the beginning.
this is the output in console window.

chk_array [0] [1]
chk_array [1] [6] <--|
chk_array [2] [3] | These two numbers are not supposed to be the same They should be
chk_array [3] [2] | different.
chk_array [4] [6] <--|
chk_array [5] [8]
chk_array [6] [0] <--|
chk_array [7] [0] <--| Similarly these are also not supposed to be the same.
chk_array [8] [1]
^
^
^
This is the array number

Now u know what my problem is. I need all different numbers. Please help me out.

D

[BiT]

Something like this is what you are looking for

include <iostream>

include <time.h>

define MAXNUMBER 9

using namespace std;

//Random Number Generator
int RandomNumberGenerator(){
return rand() % 8;
}

int main(int argc, char ** argv)
{
// Generate random seed
srand(time(0));
// initialize array
int NumbersGenerated[MAXNUMBER][1];
for(int i=0;i< MAXNUMBER; i++){
// set array element to 0 or false
NumbersGenerated[i][0] = 0;
}
for(int j=0; j<MAXNUMBER;j++){
//holder for random generated number
int temp;
//used to exit while loop
bool isUsed = false;
while(isUsed==false){
//set temp to generated number
temp = RandomNumberGenerator();
// check to see if it is false or has been used
if(NumbersGenerated[temp][0] == 0){
// set to true
NumbersGenerated[temp][0] = 1;
// tell our while loop to exit
isUsed=true;
// print it out
cout << temp << endl;
}
}
}

system("pause");

return(0);
}

[BiT]

my bad...not enough coffee yet

return rand() % 8;

should be

return rand() % 9;

[cpns]

You misunderstand the meaning of "random".

If every number in the sequence were unique, it would not be random, once you'd drawn a 6, 6 would have a liklihood of zero, and the liklihood of any other number not yet drawn increases equally. That's not random by any definition!

You are looking for a random order of non random values, not random values. You need a shuffle algorithm. http://en.wikipedia.org/wiki/Knuth_shuffle

rand() produces a random number not a random order, moreover the chances are that in that short loop it is producing a unique number each time but the %9 operation is restricting the value to a small range. (12 % 9) has the same value as (21 % 9) for example, each is equally likley on each iteration. Even then if rand() produces n it is equally likley to produce another n as it is any other value - that is what random means - all values have an equal liklihood, without any influence from historical values.

Clifford

[cpns]

>> I am darkshade...

Hello Mathew Thomas ;-)

That is why I created a new account. Sourceforge has a distict lack of respect for personal privacy. It was not always thus, they changed it after I joined up and without asking... <very rude word here>.