ex-18-08

Programming Csharp Source Code(代码) Programming Csharp Source Code

// Example 18-08: Comparing loop to brute force

namespace Programming_CSharp
{
   using System;
   using System.Diagnostics;
   using System.Threading;

   public class MyMath
   {
      // sum numbers with a loop
      public int DoSum(int n)
      {
         int result = 0;
         for(int i = 1; i <= n; i++)
         {
            result += i;
         }
         return result;
      }

      // brute force by hand
      public int DoSum2()
      {
         return 1+2+3+4+5+6+7+8+9+10+11
            +12+13+14+15+16+17+18+19+20;
      }

   }

   public class TestDriver
   {
      public static void Main()
      {

         const int val = 20;  // val to sum

         // 1,000,000 iterations
         const int iterations = 1000000;

         // hold the answer
         int result = 0;

         MyMath m = new MyMath();            

         // mark the start time   
         DateTime startTime = DateTime.Now;

         // run the experiment
         for (int i = 0;i < iterations;i++)
         {
            result = m.DoSum(val);
         }
         // mark the elapsed time
         TimeSpan elapsed = 
            DateTime.Now - startTime;

         // display the results
         Console.WriteLine(
            "Loop: Sum of ({0}) = {1}",
               val, result);
         Console.WriteLine(
            "The elapsed time in milliseconds is: " + 
            elapsed.TotalMilliseconds.ToString());

         // mark a new start time
         startTime = DateTime.Now;

         // run the experiment
         for (int i = 0;i < iterations;i++)
         {
            result = m.DoSum2();
         }

         // mark the new elapsed time
         elapsed = DateTime.Now - startTime;

         // display the results
         Console.WriteLine(
            "Brute Force: Sum of ({0}) = {1}",
               val, result);
         Console.WriteLine(
            "The elapsed time in milliseconds is: " + 
            elapsed.TotalMilliseconds);
      }
   }
}