Dice Rolling Problem

Roll 2 dice 36000 times and tally the results using an array.

I'm very confused.

My program:

Code:

---

#include <iostream>

using std::cout;
using std::cin;

#include <cstdlib>

#include <ctime>


int roll_die( int );
void display( int [] );

int main()
{
    int roll1;
    int roll2;
    int total;
    int num[ 11 ];

    srand( time( 0 ) );

    for ( int a = 0; a < 36000; a++ ) {

        roll1 = roll_die( roll1 );
        roll2 = roll_die( roll2 );

        total = roll1 + roll2;

        num[ total - 1 ] = 1;

    }

    display( num );

    cin.get();
    return 0;
}

int roll_die( int roll )
{
    roll = 1 + rand() % 6;
    return roll;
}


void display( int number [] )
{
    for ( int b = 0; b < 12; b++ )
        cout << b + 1 << " was rolled " << number[ b ] << " times.\n";
}

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My output:

Code:

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1 was rolled 2009252814 times.
2 was rolled 1 times.
3 was rolled 1 times.
4 was rolled 1 times.
5 was rolled 1 times.
6 was rolled 1 times.
7 was rolled 1 times.
8 was rolled 1 times.
9 was rolled 1 times.
10 was rolled 1 times.
11 was rolled 1 times.
12 was rolled 1 times.

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I understand that I might be doing this completely wrong; I haven't programmed in months, and I wasn't very good at it in the first place!

Code:

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  num[ total - 1 ] = 1;

---

You never change the elements of num[] anywhere else. The value of num[0] is an uninitialized value, since you don't initialize the elements of num[] to zero and total is never 1. Also, roll_die() should be declared as

Code:

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int roll_die()

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and the variable roll should be a local variable in the function body, since you never use the value you're presently passing.

Edit: Just to be clear, what you need to do is INCREMENT num[total-1], not set it to 1:

Code:

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  ++num[total-1];

---

but don't forget to initialize all the elements of num[] to 0 first.

Edit: It should also be

Code:

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  int num[12];

---

Edit: The guaranteed maximum value of a signed short or int is only 32767, but num[] should be a type with a guaranteed maximum of at least 36000. An unsigned short or int has a guaranteed maximum of 65535. Of course, it's very unlikely (read "lifetime-of-the-universe unlikely") that you would get a single value more than 32767 times with 36000 rolls, but still.

Code:

---

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

using namespace std;

int roll_die();
void display( int [] );

//This is kind of stupid, but whatever
const int MAX_SUM = 6 + 6;
const int NUM_ROLLS = 36000;


int main()
{
    int num[MAX_SUM];

    srand( time( 0 ) );

    for (int i = 0; i < MAX_SUM; i++)
            num[i] = 0;

    for ( int a = 0; a < 36000; a++ )
            num[roll_die() + roll_die() - 1]++;
   
    display( num );
 
}



int roll_die( )
{
    int roll = (rand() &#37; 6) + 1;
    return roll;
}


void display( int number [] )
{
    //Notice I changed b's initial value to 1
    for ( int b = 1; b < 12; b++ )
        cout << b + 1 << " was rolled " << number[ b ] << " times.\n";
}

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Thanks, robatino, the problem was that I didn't initialize. Agh that was supposed to say += not = !!! Haha thats why I got all those 1's :)