Topic: 7 Common Mistakes Made By C# Programmers

[Kerry]

7 Common Mistakes Made By C# Programmers

http://www.codeguru.com/csharp/csharp/cs_misc/article.php/c17911__1/7-Common-Mistakes-Made-By-C-Programmers.htm

Article came in on my news feed, thought it worth passing on unread.

[David Hall]

Good article, I learned a better way use For and Foreach

[Kerry]

yes David, that looks worthy of testing.

I notice he doesn't use either:

watch.Reset();
or
watch = Stopwatch.StartNew();
 
 ... so the timer is not restarted

Perhaps it should have been tested with a variable quantum of elements to better demonstrate his hypothesis.

[Kerry]

I had a little play ...

Code: [Select]


// CodeHimBelonga kdub@theSwamp 20100914

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Data;

namespace ForeachTester
{
    class Program
    {
        static void Main(string[] args)
        {
            DataTable dt = new DataTable();
            DataColumn col1 = new DataColumn("Id", typeof(int));
            col1.AutoIncrement = true;
            DataColumn col2 = new DataColumn("Name", typeof(string));
            DataColumn col3 = new DataColumn("TimeStamp", typeof(DateTime));           

            dt.Columns.AddRange(new DataColumn[] { col1, col2, col3 });

            dt.Rows.Add(null, "John", DateTime.Now   );
            dt.Rows.Add(null, "George", DateTime.Now );
            dt.Rows.Add(null, "Paul", DateTime.Now   );
            dt.Rows.Add(null, "Ringo", DateTime.Now  );

            Stopwatch watch = new Stopwatch();

            //For loop
            watch.Start();
            for (int count = 0; count < dt.Rows.Count; count++)
            {
                dt.Rows[count]["Name"] = "Modified in For";
            }
            watch.Stop();

            // The smallest unit of time is the tick, which is equal to 100 nanoseconds.
            Console.WriteLine("Ticks taken in For loop: {0}", watch.Elapsed.Ticks);
            watch.Reset();

            //Foreach loop
            watch.Start();
            foreach (DataRow row in dt.Rows)
            {
                row["Name"] = "Modified in ForEach";
            }
            watch.Stop();
            Console.WriteLine("Ticks taken in For Each loop: {0 }", watch.Elapsed.Ticks);

            Console.ReadKey();
        }
    }
}



[Kerry]

Just to show that you can sometimes believe some parts of some things that you read ...
<except for : see next post>

Code: [Select]

// CodeHimBelonga kdub@theSwamp 20100914

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Data;

namespace ForeachTester
{
    class Program
    {
        static void Main(string[] args)
        {
            DataTable dt = new DataTable();
            DataColumn col1 = new DataColumn("Id", typeof(int));
            col1.AutoIncrement = true;
            DataColumn col2 = new DataColumn("Name", typeof(string));
            DataColumn col3 = new DataColumn("TimeStamp", typeof(DateTime));          

            dt.Columns.AddRange(new DataColumn[] { col1, col2, col3 });

            for (int count = 0; count < 1000 ; count++)
            {
                dt.Rows.Add(null, count.ToString(), DateTime.Now);
            }

            Stopwatch watch = new Stopwatch();

            //For loop
            watch.Start();
            for (int count = 0; count < dt.Rows.Count; count++)
            {
                dt.Rows[count]["Name"] = "Modified in For";
            }
            watch.Stop();

            // The smallest unit of time is the tick, which is equal to 100 nanoseconds.
            Console.WriteLine("Ticks taken in For loop: {0}", watch.Elapsed.Ticks);
            watch.Reset();

            //Foreach loop
            watch.Start();
            foreach (DataRow row in dt.Rows)
            {
                row["Name"] = "Modified in ForEach";
            }
            watch.Stop();
            Console.WriteLine("Ticks taken in For Each loop: {0 }", watch.Elapsed.Ticks);

            Console.ReadKey();
        }
    }
}


[Kerry]

... but not always

Code: [Select]

            for (int count = 0; count < 5000 ; count++)
            {
                dt.Rows.Add(null, count.ToString(), DateTime.Now);
            }
            Console.WriteLine("Row Count: {0 }", dt.Rows.Count);


[Kerry]

so I s'pose No 8 is :
Failure to test presumptions , yes ?

[David Hall]

WOW, what made it flipFlop over itself?

[Bryco]

Running the code twice gives very different results. It must be retaining something in memory.
Putting the foreach above the for gives a slightly worse result.
 

[Jeff H]

 I believe you need to run the for and foreach in different programs because the Just in Time (JIT) realizes it is running over the same collections especially if you do it twice. And I thought I read somewhere foreach is faster for non-generic List and arrays. I can not remeber what I worked on yesterday so do not hold me to that.
I will try to find where I read this

[Kerry]

ok, to try to even out the testing,

I've made duplicate DataTables and run each timed test twice

The results seem proportionately consistant.
Keep in mind this is timed in Ticks [of 100 nanoseconds]

Code: [Select]


// CodeHimBelonga kdub@theSwamp 20100915

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Data;

namespace ForeachTester
{
    class Program
    {
        static void Main(string[] args)
        {
            DataTable dt1 = new DataTable();
            DataColumn col1 = new DataColumn("Id", typeof(int));
            col1.AutoIncrement = true;
            DataColumn col2 = new DataColumn("Name", typeof(string));
            DataColumn col3 = new DataColumn("TimeStamp", typeof(DateTime));          

            dt1.Columns.AddRange(new DataColumn[] { col1, col2, col3 });

            for (int count = 0; count < 5000 ; count++)
            {
                dt1.Rows.Add(null, count.ToString(), DateTime.Now);
            }
            Console.WriteLine("Row Count: {0 }", dt1.Rows.Count);
            
            DataTable dt2;
            dt2 = dt1.Copy();

            Stopwatch watch = new Stopwatch();

            //For loop
            watch.Start();
            for (int count = 0; count < dt2.Rows.Count; count++)
            {
                dt2.Rows[count]["Name"] = "Modified in For";
            }
            watch.Stop();
            // The smallest unit of time is the tick, which is equal to 100 nanoseconds.
            Console.WriteLine("Ticks taken in For loop DT2    : {0}", watch.Elapsed.Ticks);
            watch.Reset();

            //Foreach loop
            watch.Start();
            foreach (DataRow row in dt1.Rows)
            {
                row["Name"] = "Modified in ForEach";
            }
            watch.Stop();
            Console.WriteLine("Ticks taken in ForEach loop DT1: {0 }", watch.Elapsed.Ticks);
            watch.Reset();

            //For loop
            watch.Start();
            for (int count = 0; count < dt2.Rows.Count; count++)
            {
                dt2.Rows[count]["Name"] = "Modified in For";
            }
            watch.Stop();
            // The smallest unit of time is the tick, which is equal to 100 nanoseconds.
            Console.WriteLine("Ticks taken in For loop DT2    : {0}", watch.Elapsed.Ticks);
            watch.Reset();

            //Foreach loop
            watch.Start();
            foreach (DataRow row in dt1.Rows)
            {
                row["Name"] = "Modified in ForEach";
            }
            watch.Stop();
            Console.WriteLine("Ticks taken in ForEach loop DT1: {0 }", watch.Elapsed.Ticks);
            watch.Reset();


            Console.ReadKey();
        }
    }
}