Rolling a Six-Sided Die 6,000,000 Times

To show that the numbers produced by rand occur with approximately equal likelihood, Fig. 6.8 simulates 6,000,000 rolls of a die. Each integer in the range 1 to 6 should appear approximately 1,000,000 times. This is confirmed by the program’s output.

Click here to view code image

 1   // Fig. 6.8: fig06_08.cpp
 2   // Rolling a six-sided die 6,000,000 times.
 3   #include <iostream>
 4   #include <iomanip>
 5   #include <cstdlib> // contains function prototype for rand
 6   using namespace std;
 7
 8   int main()
 9   {
10      unsigned int frequency1 = 0; // count of 1s rolled
11      unsigned int frequency2 = 0; // count of 2s rolled
12      unsigned int frequency3 = 0; // count of 3s rolled
13      unsigned int frequency4 = 0; // count of 4s rolled
14      unsigned int frequency5 = 0; // count of 5s rolled
15      unsigned int frequency6 = 0; // count of 6s rolled
16
17      // summarize results of 6,000,000 rolls of a die
18      for ( unsigned int roll = 1; roll <= 6000000; ++roll )
19      {
20         unsigned int face = 1 + rand() % 6; // random number from 1 to 6
21
22         // determine roll value 1-6 and increment appropriate counter
23         switch ( face )
24         {
25            case 1:
26               ++frequency1; // increment the 1s counter
27               break;
28            case 2:
29               ++frequency2; // increment the 2s counter
30               break;
31            case 3:
32               ++frequency3; // increment the 3s counter
33               break;
34            case 4:
35               ++frequency4; // increment the 4s counter
36               break;
37            case 5:
38               ++frequency5; // increment the 5s counter
39               break;
40            case 6:
41               ++frequency6; // increment the 6s counter
42               break;
43            default: // invalid value
44               cout << "Program should never get here!";
45         } // end switch
46      } // end for
47
48      cout << "Face" << setw( 13 ) << "Frequency" << endl; // output headers
49      cout << "   1" << setw( 13 ) << frequency1
50         << "    2" << setw( 13 ) << frequency2
51         << "    3" << setw( 13 ) << frequency3
52         << "    4" << setw( 13 ) << frequency4
53         << "    5" << setw( 13 ) << frequency5
54         << "    6" << setw( 13 ) << frequency6 << endl;
55   } // end main

Face    Frequency
   1       999702
   2      1000823
   3       999378
   4       998898
   5      1000777
   6      1000422

Fig. 6.8. Rolling a six-sided die 6,000,000 times.

As the output shows, we can simulate the rolling of a six-sided die by scaling and shifting the values produced by rand. The program should never get to the default case (lines 43–44) in the switch structure, because the switch’s controlling expression (face) always has values in the range 1–6; however, we provide the default case as a matter of good practice. After we study arrays in Chapter 7, we show how to replace the entire switch structure in Fig. 6.8 elegantly with a single-line statement.

Image Error-Prevention Tip 6.3

Provide a default case in a switch to catch errors even if you are absolutely, positively certain that you have no bugs!

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset
3.145.85.178