Random numbers

KrissKross · #1 10-May-2004, 19:06

In C how do u generate a random number between 1 and 6. I know it has something to do with the RND function from stdlib.h but I don't how to use it.

Max Payne · #2 10-May-2004, 20:21

CPP / C++ / C Code:

//seed random
srand((unsigned) time(NULL));
//get random
int tmp=rand()%6+1;

dsmith · #3 10-May-2004, 20:34

You do have to include stdlib.h as well.

Also, keep in mind that you should only seed the random number function once in your program or you may get unrandom random numbers. There are several posts here that discuss this, but there is nothing really random about the random numbers that this function will give you. When you seed the number generator it selects a predefined list of numbers based on that seed. So if you seed it with the same number, your sequence will always be identical.

Cheers,
d

KrissKross · #4 13-May-2004, 17:51

Hmm didnt realy work, I need my program to generate 5 different random numbers and assingn them to elements 0 through 4 of an array. When I run the program it always generates the same number for all 5 elements. Is there some way I can generate 5 different random numbers? My program needs to be able to simulate 5 dice and I cant have them all being 1 or 4 or 6.

machinated · #5 13-May-2004, 18:49

put srand(time(NULL)); at the very beginning of your program. and then whenever you need random numbers, just use the rand() function. you must use srand function only once in your program!

dsmith · #6 13-May-2004, 20:31

Quote:

Originally Posted by KrissKross

Hmm didnt realy work, I need my program to generate 5 different random numbers and assingn them to elements 0 through 4 of an array. When I run the program it always generates the same number for all 5 elements. Is there some way I can generate 5 different random numbers? My program needs to be able to simulate 5 dice and I cant have them all being 1 or 4 or 6.

A random number is just a random number there is no guarantee that you will get just a single number in a selection set, in fact it would be pretty rare. What you need to do is to set up a loop that will check the previous numbers to see if they are similar. Something like:

CPP / C++ / C Code:

srand((unsigned) time(NULL));
for(x=0;x<5;x++){
  numbers[x] = rand()%6+1;
  same = 0;
  do{
    for(y=0;y<x;y++){
      if(numbers[x] == numbers[y]){
        same = 1;
        break;
      }
    }
  }while(!same);
}

Thats written on the fly (I didn't compile it), but it should give you the idea.

HTH,
d

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