Rolling a Six-Sided Die

Figure 6.11 uses the default_random_engine and the uniform_int_distribution to roll a six-sided die. Line 14 creates a default_random_engine object named engine. Its constructor argument seeds the random-number generation engine with the current time. If you don’t pass a value to the constructor, the default seed will be used and the program will produce the same sequence of numbers each time it executes. Line 15 creates randomInt—a uniform_int_distribution object that produces unsigned int values (as specified by <unsigned int>) in the range 1 to 6 (as specified by the constructor arguments). The expression randomInt(engine) (line 21) returns one unsigned int value in the range 1 to 6.

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 1   // Fig. 6.11: fig06_11.cpp
 2   // Using a C++11 random-number generation engine and distribution
 3   // to roll a six-sided die.
 4   #include <iostream>
 5   #include <iomanip>
 6   #include <random> // contains C++11 random number generation features
 7   #include <ctime>
 8   using namespace std;
 9
10   int main()
11   {
12      // use the default random-number generation engine to                
13      // produce uniformly distributed pseudorandom int values from 1 to 6 
14      default_random_engine engine( static_cast<unsigned int>( time(0) ) );
15      uniform_int_distribution<unsigned int> randomInt( 1, 6 );            
16
17      // loop 10 times
18      for ( unsigned int counter = 1; counter <= 10; ++counter )
19      {
20         // pick random number from 1 to 6 and output it
21         cout << setw( 10 ) << randomInt( engine );
22
23         // if counter is divisible by 5, start a new line of output
24         if ( counter % 5 == 0 )
25            cout << endl;
26      } // end for
27   } // end main

         2         1         2         3         5
         6         1         5         6         4

Fig. 6.11. Using a C++11 random-number generation engine and distribution to roll a six-sided die.

The notation <unsigned int> in line 15 indicates that uniform_int_distribution is a class template. In this case, any integer type can be specified in the angle brackets (< and >). In Chapter 18, we discuss how to create class templates and various other chapters show how to use existing class templates from the C++ Standard Library. For now, you should feel comfortable using class template uniform_int_distribution by mimicking the syntax shown in the example.

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