Random Numbers in C++

Question

I'm creating a BlackJack Program. I want the cards to be randomly dealt. if i use the rand() function and initialize srand() to time(NULL) then all the cards turn out to be same. Any idea what the problem might be ?

//Cards.h
#include <iostream>
#include <time.h>
#include <cstdlib>
using namespace std;

class Cards
{
      private:
      int val_seed,suit_seed;
      public:
      int val[10];
      string card[10];
      int dealcard(int x)
      {   
          srand(); 
          val_seed=rand()%13 + 2;
          suit_seed=rand()%4 + 1;
          if(val_seed>=1 && val_seed<=10)
          {
                  if(val_seed==10)
                  {
                                  card[x]="10";
                  }
                  else
                  {
                      card[x]=val_seed+48;
                  }
          }
          else if(val_seed>10)
          {
               switch(val_seed)
               {
                               case 11: card[x]="J"; val_seed=10; break;
                               case 12: card[x]="Q"; val_seed=10; break;
                               case 13: card[x]="K"; val_seed=10; break;
                               case 14: card[x]="A"; val_seed=11; break;
               }
          }
          switch(suit_seed)
          {
                           case 1: card[x]+='\3'; break;
                           case 2: card[x]+='\4'; break;
                           case 3: card[x]+='\5'; break;
                           case 4: card[x]+='\6'; break;
          }
          val[x]=val_seed;
      }

};
//main.cpp
#include <cstdlib>
#include <iostream>
#include "Cards.h"

using namespace std;

int main(int argc, char *argv[])

{
    Cards k;
    for(int a=1; a<=9; a++)
    {
            k.dealcard(a);
    }

    for(int e=1; e<=9; e++)
    {
            cout<<k.card[e]<<"("<<k.val[e]<<")"<<" ";
    }

    cout<<endl;
    system("PAUSE");
    return EXIT_SUCCESS;
}

Answer 1

Seed the number generator ONCE. If you run your function in a loop they will be executed faster than the time resolution interval (so all the seeds are the same and therefore the numbers).

While developing the app and debugging it it will help if you seed the generator with the same, known value. This means successive debugging sessions will use the same values from the generator. Don't forget to switch back to a time() based seed in your release build (or use the pre-processor to detect if it's a Debug or Release build and do it for you).