probability of dice throw

This is a discussion on probability of dice throw within the C Programming forums, part of the General Programming Boards category; I have wriiten the following code that generates a random dice throw 36000 times. It then prints out the number ...

  1. #1
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    probability of dice throw

    I have wriiten the following code that generates a random dice throw 36000 times. It then prints out the number of times each pair is thrown. I want to also output the actual and expected probabilities fo each throw. Do I need another for loop to jump through the array, or what am i missing here. Any help would be greatly appreciated. Thanks to all the people who are smarter than the average bear.

    code:

    #include<stdio.h>
    #include<stdlib.h>
    #include<time.h>
    #define SIZE 13 /*0-12*/

    int main ()
    {
    int die_one, die_two, roll,j,sum, freq[SIZE] = {0};
    float actual;

    srand(time(NULL));

    for (roll= 1; roll <= 36000; roll++)
    {
    die_one = rand () % 6 +1;
    die_two = rand () % 6 +1;
    sum = die_one + die_two;
    ++freq [sum];

    }



    printf("%s%10s%20s%22s\n", "Sum", "Freq", "Expected", "Actual");

    for (sum =2; sum <= SIZE -1; sum++)
    {
    printf("%2d%10d%20f\n", sum, freq[sum], actual);

    }
    return 0;
    }

    Sum Freq Expected Actual
    2 947
    3 2034
    4 2998
    5 4063
    6 5075
    7 5889
    8 4986
    9 4005
    10 2943
    12 1020
    Press any key to continue

  2. #2
    and the hat of wrongness Salem's Avatar
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    > I want to also output the actual and expected probabilities fo each throw
    Well the expected probablility is what you get from reading any statistics book.
    You can pre-initialise an array with these values

    Something like this, with numbers to suit
    int expected[SIZE] = { 1, 2, 3, 4, 5, 6, 7 };

    The actual results are all in freq[sum]

    So your print statement would be
    printf("%2d%10d%10d\n", sum, expected[sum], freq[sum] );

  3. #3
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    Your expected array is [1k, 2k, 3k, 4k, 5k, 6k, 5k, 4k, 3k, 2k, 1k]. Let us know if you need more info.

  4. #4
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    Hi,
    How's everyone doing? I have a basic knowledge of C, therefore, I decided to participate in some questionaires regarding C. In the booklet I came across the following program. Although I have compiled this several times- Turbo C & DJGPP, I receive some errors. Let's have a look together..

    /* Roll a six-sided dice 6000 times */

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

    int main()
    {

    int face, roll, frequency1 = 0, frequency2 = 0,
    frequency3 = 0, frequency4 = 0,
    frequency5 = 0, frequency6 = 0;

    for ( roll = 1; roll <= 6000; roll++ )
    face = 1 + rand() % 6;

    switch ( face )
    {

    case 1:
    ++frequency1;
    break;
    case 2:
    ++frequency2;
    break;
    case 3:
    ++frequency3;
    break;
    case 4:
    ++frequency4;
    break;
    case 5:
    ++frequency5;
    break;
    case 6:
    ++frequency6;
    break;

    }

    }

    printf( "%s%13s\n", "Face", "Frequency" );
    printf( " 1%13d\n", frequency1 );
    printf( " 2%13d\n", frequency2 );
    printf( " 3%13d\n", frequency3 );
    printf( " 4%13d\n", frequency4 );
    printf( " 5%13d\n", frequency5 );
    printf( " 6%13d\n", frequency6 );

    return 0;

    }

    Could you compile this? Please let me know the result. I'd be thankful.

    Al - IRAN..

  5. #5
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    you had too many brackets.

    Code:
    /* Roll a six-sided dice 6000 times */ 
    
    #include <stdio.h> 
    #include <stdlib.h> 
    
    int main(void) 
    { 
     int face, roll, frequency1 = 0, frequency2 = 0, 
     frequency3 = 0, frequency4 = 0, 
     frequency5 = 0, frequency6 = 0; 
    
     for ( roll = 1; roll <= 6000; roll++ ) 
     {
      face = 1 + rand() % 6; 
    
      switch ( face ) 
      { 
        case 1: 
         frequency1++; 
        break; 
        case 2: 
         frequency2++; 
        break; 
        case 3: 
         frequency3++; 
        break; 
        case 4: 
         frequency4++; 
        break; 
        case 5: 
         frequency5++; 
        break; 
        case 6: 
         frequency6++; 
        break; 
      }
     }   
     printf( "%s%13s\n", "Face", "Frequency" ); 
     printf( " 1%13d\n", frequency1 ); 
     printf( " 2%13d\n", frequency2 ); 
     printf( " 3%13d\n", frequency3 ); 
     printf( " 4%13d\n", frequency4 ); 
     printf( " 5%13d\n", frequency5 ); 
     printf( " 6%13d\n", frequency6 ); 
     return 0; 
    }
    edit: and information on getting better randomness is in the FAQ.
    Last edited by Brian; 02-18-2002 at 05:59 PM.

  6. #6
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    Thanks for everything guys. Your solutions were insightful and helpful.

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