Help with C Monte Carlo

i guys,

I'm trying to make a simple Monte Carlo simulation for a class. It requires that I make a roulette game with random numbers.

So far:

There needs to be 1000 games max. You can bet $1 on the game and continue playing until you loose (black and red are wins) .

The statistics are:
Black 0-0.4737
Red Same
Green 0 to .0526.

Because rand() only uses integers. I multiplied the probabilities times 1000.

My code is as follows:

Code:

---


#include <stdio.h> //std input and output
#include <conio.h>
#include <math.h> //math library
#include <stdlib.h> //standard libarary

int main (void)
{
 printf("Welcome To The Roulette Wheel Simulator. \n");
    int counter = 0; //count the number of games
    int cash = 0; //count the number of $1 you win.
    int p = 0; //probability is an integer here to allow for rand.
    double probability = 0; //hasn't been used yet.
    int games = 0;
//pseudo-random number generator
          while (counter <1000) {
              counter = counter + 1;
              p = rand()%4737+1000;
                                              }
                while(p > 526 && counter <1000) //continue to loop until a loss
                    {
                          counter = counter + 1; //increment counter.
                          cash = cash + 1; //add to cash.
                      }
          if(p <= 526)
              {
                  printf("Once you kill a cow, you gotta' make a burger. _GaGa_ \n You lost at %d games\n You won $%d \n", &counter, &cash);
                  printf ("I knew you'd steal all my honey, you selfish (imagination here). _Beyonce_ \n Press Any Key to Exit says Homer\n");
              }
              getch();
}

---

It complies but never prints anything.

Code:

---

          while (counter <1000) {
              counter = counter + 1;
              p = rand()%4737+1000;
                                              }

---

This keeps anything from being done. First of all, this loop ensures that counter will be 1000 once the loop is over, which means that the "while(p > 526 && counter <1000)" loop will never run. Also, because of the assignment to p, namely the random number + 1000, p is always going to be greater than 1000, so "if(p <= 526)" will always be false.

Code:

---

#include <stdio.h> //std input and output
   
    #include <math.h> //math library
    #include <stdlib.h> //standard libarary
   
    int main (void)
    {
        printf("Welcome To The Roulette Wheel Simulator. \n \n");
        long cash = 0; //count the number of $1 you win.
        int p = 0;  //probability is an integer here to allow for rand.
        double probability = 0; //hasn't been used yet.
        int games = 0; 
        //pseudo-random number generator
      int counter;
      for(counter = 0; counter < 1000; counter++)
        {
            int p = 0;
            p = rand()%4737;
       
            if(p >= 526  && counter < 1000) //continue to loop until a loss
            {   
                cash = cash + 1; //add to cash.
            }
            if(p <= 526)
            {
                printf(" You lost at %d games\n \n You won $%d \n \n", &counter, &cash);
                printf ("Press Any Key to Exit\n");
                break;
            }
           
        }
        getch();
    }

---

Tried to fix it, still not working. thankx for the help

Code:

---

#include <stdio.h> //std input and output
#include <math.h> //math library
#include <stdlib.h> //standard libarary

int main (void)
{
  printf("Welcome To The Roulette Wheel Simulator. \n \n");
  long cash = 0; //count the number of $1 you win.
  int p = 0;  //probability is an integer here to allow for rand.
  double probability = 0; //hasn't been used yet.
  int games = 0; 
  //pseudo-random number generator
  int counter;
  for(counter = 0; counter < 1000; counter++)
  {
    int p = 0;
    p = rand()%4737;
   
    if(p >= 526  && counter < 1000) //continue to loop until a loss
    {   
      cash = cash + 1; //add to cash.
    }
    if(p <= 526)
    {
      printf(" You lost at %d games\n \n You won $%d \n \n", &counter, &cash);
      printf ("Press Any Key to Exit\n");
      break;
    }
  }
  getch();
}

---

1. Learn indentation - SourceForge.net: Indentation - cpwiki

2. && counter < 1000 will never happen, given the for loop has the same test.

3. >= 526 and <= 526 overlap at 526. It would have been better to use an else

4. &counter, &cash - you have to pay attention to what you pass to printf/scanf.
printf(" You lost at %d games\n \n You won $%ld \n \n", counter, cash);

Quote:

---

Originally Posted by Salem

[code]
2. && counter < 1000 will never happen, given the for loop has the same test.
[/FONT]

---

Surely you must mean it WILL ALWAYS HAPPEN, BECAUSE it is inside the loop, therefore the loop condition is still true. It is useless, but in no case false.

> It is useless, but in no case false.
Yes :eek:

I cleaned up the code and indentation. The problem was the algorithm itself. The code now runs fine; however, the rand() seems to generate the same set of numbers, causing the same number of wins and losses each time. I tried printf on p and it keeps generating the same "random" numbers.

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>


int
main (void)
{
  int p = 0;
  int losses = 0;
  int wins = 0;
  int counter_Black = 0;
  int counter_Red = 0;
  int counter_Green = 0;
  int counter = 0;
  for (counter; counter < 1001; counter++)
    {
      p = rand () % 10000;
      if (p <= 4736)
        {
          counter_Black = counter_Black + 1;
          wins = wins + 1;
        }
      if (p > 4736 && p <= 9473)
        {
          counter_Red = counter_Red + 1;
          wins = wins + 1;
          if (p > 9473 && p <= 10000)
            counter_Green = counter_Green + 1;
          losses = losses + 1;
        }
    }
  printf ("You won $%d after %d games.\nYou had %d losses. \n \n ", wins,
          wins, losses);
  getch ();
}

---

You need to seed the random generator with the current time.

Seed rand() with the system time and display the first 10 numbers : Random « Math « C / ANSI-C