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diff --git a/chapter8/washing.cxx b/chapter8/washing.cxx
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+// FILE: washing.cxx
+// CLASSES implemented: bool_source, averager, washer
+//
+// INVARIANT for the bool_source ADT:
+//   1. The member variable probability is the appoximate probability that
+//      query( ) returns true.
+//
+// INVARIANT for the averager ADT:
+//   1. The member variable count indicates how many numbers the averager has
+//      been given.
+//   2. The member variable sum is the sum of all the numbers that the
+//      averager has been given.
+//
+// INVARIANT for the washer class:
+//   1. The member variable seconds_for_wash is the number of seconds required
+//      for one wash.
+//   2. The member varible wash_time_left is 0 if the washer is not busy;
+//      otherwise it is the number of seconds until the washer is free.
+
+#include <cassert>    // Provides assert
+#include <cstdlib>    // Provides rand, RAND_MAX, size_t
+#include "washing.h"  // Provides bool_source, averager, washer definitions
+using namespace std;
+
+namespace main_savitch_8A
+{
+    bool_source::bool_source(double p)
+    // Library facilities used: cassert
+    {
+        assert(p >= 0);
+        assert(p <= 1);
+        probability = p;
+    }
+
+    bool bool_source::query( ) const
+    // Library facilities used: cstdlib
+    {
+        return (rand( ) < probability * RAND_MAX);
+    }
+
+    averager::averager( )
+    {
+        count = 0;
+        sum = 0;
+    }
+
+    void averager::next_number(double value)
+    {
+        ++count;
+        sum += value;
+    }
+    
+    double averager::average( ) const
+    // Library facilities used: cassert
+    {
+        assert(how_many_numbers( ) > 0);
+        return sum/count;
+    }
+    
+    washer::washer(unsigned int s)
+    {
+        seconds_for_wash = s;
+        wash_time_left = 0;
+    }
+
+    
+    void washer::one_second( )
+    {
+        if (is_busy( ))
+            --wash_time_left;
+    }
+
+    
+    void washer::start_washing( )
+    // Library facilities used: cassert
+    {
+        assert(!is_busy( ));
+        wash_time_left = seconds_for_wash;
+    }
+}