From c1b6ffe70bd281c6c230fd63fabcaac2aff47514 Mon Sep 17 00:00:00 2001
From: Fuwn <contact@fuwn.me>
Date: Sun, 7 Apr 2024 23:18:32 -0700
Subject: feat: initial commit

---
 chapter14/pondlife.cxx | 126 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 126 insertions(+)
 create mode 100644 chapter14/pondlife.cxx

(limited to 'chapter14/pondlife.cxx')

diff --git a/chapter14/pondlife.cxx b/chapter14/pondlife.cxx
new file mode 100644
index 0000000..87fc20e
--- /dev/null
+++ b/chapter14/pondlife.cxx
@@ -0,0 +1,126 @@
+// FILE: pondlife.cxx
+// A simple simulation program to model the fish and weeds in a pond
+
+#include <iostream>    // Provides cin, cout
+#include <iomanip>     // Provides setw
+#include <cstdlib>     // Provides EXIT_SUCCESS, rand, size_t
+#include <vector>      // Provides the vector template class
+#include "organism.h"  // Provides Herbivore, Plant classes
+using namespace std;
+using namespace main_savitch_14;
+
+// PROGRAM CONSTANTS
+const size_t MANY_WEEDS      = 2000; // Number of weeds in the pond
+const double WEED_SIZE       =   15; // Initial size of each weed, in ounces
+const double WEED_RATE       =  2.5; // Growth rate of weeds, in ounces/week
+const size_t INIT_FISH       =  300; // Initial number of fish in the pond
+const double FISH_SIZE       =   50; // Fish size, in ounces
+const double FRACTION        =  0.5; // A fish must eat FRACTION times its size
+                                     // during one week or it will die.
+const int    AVERAGE_NIBBLES =   30; // Average number of plants nibbled by
+                                     // a fish over one week.
+const double BIRTH_RATE      = 0.05; // At the end of each week, some fish have
+                                     // babies. The total number of new fish
+                                     // born is the current number of fish times
+                                     // the BIRTH_RATE (rounded down to an
+                                     // integer).
+
+// Samples weed and fish objects to copy into the vectors of the main program:
+const plant SAMPLE_WEED(WEED_SIZE, WEED_RATE);
+const herbivore SAMPLE_FISH(FISH_SIZE, 0, FISH_SIZE * FRACTION);
+
+// PROTOTYPES for the functions used in the program:
+void pond_week(vector<herbivore>& fish, vector<plant>& weeds);
+// Precondition: weeds.size( ) > 0.
+// Postcondition: On average, each fish has nibbled on AVERAGE_NIBBLES plants,
+// and then simulate_week has been activated for each fish and each weed. Any
+// fish that died are removed from the fish bag, and then
+// BIRTH_RATE * fish.size( ) new fish have been added to the fish bag.
+
+double total_mass(const vector<plant>& collection);
+// Postcondition: The return value is the total mass of all the plants in the
+// collection.
+
+    
+int main( )
+{
+    vector<plant> weeds(MANY_WEEDS, SAMPLE_WEED);    // A vector of weeds
+    vector<herbivore> fish(INIT_FISH, SAMPLE_FISH);  // A vector of weeds
+    int many_weeks;   // Number of weeks to simulate
+    int i;            // Loop control variable
+
+    // Get number of weeks, and format the output.
+    cout << "How many weeks shall I simulate? ";
+    cin >> many_weeks;
+    cout.setf(ios::fixed);
+    cout << "Week    Number    Plant Mass" << endl;
+    cout << "       of Fish   (in ounces)" << endl;
+
+    // Simulate the weeks.
+    for (i = 1; i <= many_weeks; i++)
+    {
+        pond_week(fish, weeds);
+        cout << setw(4) << i;
+        cout << setw(10) << fish.size( );
+        cout << setw(14) << setprecision(0) << total_mass(weeds);
+        cout << endl;
+    }
+
+    return EXIT_SUCCESS;
+}
+
+double total_mass(const vector<plant>& collection)
+{
+    double answer;
+    vector<plant>::const_iterator p;
+    answer = 0;
+    for (p = collection.begin( ); p != collection.end( ); ++p)
+        answer += p->get_size( );
+
+    return answer;
+}
+
+void pond_week(vector<herbivore>& fish, vector<plant>& weeds)
+{
+    // Variables for an index and an iterator for the weeds:
+    vector<plant>::iterator      wi;
+    vector<plant>::size_type     weed_index;
+
+    // Variables for an index, an iterator, and counters for the fish:
+    vector<herbivore>::iterator  fi;
+    vector<herbivore>::size_type fish_index;
+    vector<herbivore>::size_type new_fish_population;
+
+    size_t many_iterations;  // How many random nibbles to simulate
+    size_t i;                // Loop counter
+
+    // Have randomly selected fish nibble on randomly selected plants.
+    many_iterations = AVERAGE_NIBBLES * fish.size( );
+    for (i = 0; i < many_iterations; ++i)
+    {
+        fish_index = rand( ) % fish.size( );  // Index of a random fish
+        weed_index = rand( ) % weeds.size( ); // Index of a random weed
+        fish[fish_index].nibble(weeds[weed_index]);
+    }
+
+    // Simulate the weeks for the weeds.
+    for (wi = weeds.begin( ); wi != weeds.end( ); ++wi)
+        wi->simulate_week( );
+
+    // Simulate the weeks for the fish, and count how many died.
+    fi = fish.begin( );
+    while (fi != fish.end( ))
+    {
+        fi->simulate_week( );
+        if (!fi->is_alive( ))
+            fish.erase(fi);
+	else
+	    ++fi;
+    }
+
+    // Calculate the new number of fish, and reset the fish vector to this size. 
+    // If this adds new fish to the vector, then those new fish will be equal to
+    // the SAMPLE_FISH that is used for all our fish:
+    new_fish_population = (1 + BIRTH_RATE) * fish.size( );
+    fish.resize(new_fish_population, SAMPLE_FISH);
+}
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