Dice Game

[bowlbase]

I'm trying to modify a dice game to run a set number of loops and give the total wins and losses. I'm using srand(time(0)) to make it random but most of the time it's just running the same dice rolls over and over again. Occasionally I'll get different rolls but they go so fast it seems like its just ignoring the time.

#include <iostream>
#include <cstdlib>
#include <ctime>

using namespace std;

int rollDice( void );  

int main()
{
   enum Status { CONTINUE, WON, LOST };
   int sum, myPoint, W = 0, L = 0;
   Status gameStatus;
for( int loop = 0; loop <= 500; ++loop){
   
   sum = rollDice();            

   switch ( sum ) {
      case 7:
   case 11:                  
         gameStatus = WON;
         break;
      case 2:
    case 3:
    case 12:                 
         gameStatus = LOST;
         break;
      default:                 
         gameStatus = CONTINUE;
         myPoint = sum;
         cout << "Point is " << myPoint << endl;
         break;                
   }

   while ( gameStatus == CONTINUE ) {    
      sum = rollDice();

      if ( sum == myPoint )       
         gameStatus = WON;
      else
         if ( sum == 7 )          
            gameStatus = LOST;
   }

   if ( gameStatus == WON )
      {++W;
      cout << "Player wins" << W << endl;}     
   else
      { ++L;
      cout << "Player loses " << L << endl;}
}      
       cout << "Total wins: " << W << endl;
       cout << "Total losses: " << L << endl;
       
   system("PAUSE");
   return EXIT_SUCCESS;
}

int rollDice( void )
{
   int die1, die2, workSum;
srand( time( 0 ) );
   die1 = 1 + rand() % 6;
   die2 = 1 + rand() % 6;
   workSum = die1 + die2;
   cout << "Player rolled " << die1 << " + " << die2
        << " = " << workSum << endl;

   return workSum;
}

[HellfireXP]

Move your srand(time(0)); outside your function and before your loop execution. It only needs to be called once at the beginning of your program, otherwise because you're calling it so fast within a loop, it will actually give you the same value every time.

[bowlbase]

Thanks that worked. I figured it was just going too fast but didn't try taking it out of the function. Appreciate the help!

[Volatile Pulse]

HellfireXP wrote:

Move your srand(time(0)); outside your function and before your loop execution. It only needs to be called once at the beginning of your program, otherwise because you're calling it so fast within a loop, it will actually give you the same value every time.

Halfway right. srand is best placed as the very first line in main, always (there is other reasons for it, but for most applications, follow that).

What does srand do? It "seeds" the rand function. rand() doesn't actually return a random value, honestly, it just seems that way. Depending on the seed, we'll get to that later, the computer gives us a number. There is a huge line of numbers somewhere telling the computer what number should be returned (obviously it doesn't work like that, but for all practical sense of it, let's pretend it does). Each time you call rand(), it reads the next number on that list.

What is a seed? A seed is, going off of the number lists I used as an example earlier, essentially the list number to use. srand accepts any unsigned int, positive number or zero. So we can write srand(5342); and every time we run the program, we will get the same exact numbers. That does us no good (it's not random enough). So instead, we pass it the return value of time(0). The function time, using 0 as a parameter, will return the number of seconds that have elapsed since January 1st, 1970. This is great since it's very unlikely that someone is going to be running the program twice in less than a second. Every second = a new seed.

So, if you're constantly calling srand then rand, you're reseeding the random numbers with the same one you just had. Now is the stuff I'm unsure of, I don't remember if time() returns the number of seconds based off of the current system time, or if it's based off of when the program was launched. Either way, srand once, and only once.

I hope this enlightened you in someway.