What is the difference between "for " and "foreach"

I always confused when should I use "for" and when foreach should be used...

when we talking about efficient which one is better to use?

thank you 

0
jcjcjc
1/23/2008 7:30:09 AM
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its quite the same just a different way howto, never done or read about big differences about the both options:

 string [] n = new string[] {"test1", "test2"}

foreach(string a in n)

  ....

for(int i=0;i< i<n.Length;++i)

  ....


regards, roni
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0
roni_schuetz
1/23/2008 8:57:52 AM

thank you , How about efficient  ? any difference between them? thank you

0
jcjcjc
1/23/2008 9:08:35 AM

Foreach is very useful in the situaltion when we need to loop though the list of objects

e.g

foreach(classname obj in listobject)

{

}

Alternatively we can use "for" here but foreach is best in this case. similarly when we need to loop through the array of variables which hols only the value then we have to use "for" option. 

 

0
vtrajan
1/23/2008 9:09:42 AM

Source MSDN:  

 In C#, the foreach keyword allows you to walk across items in a list, string, etc. and perform operations on each item. This is a very powerful tool, since it acts as a general-purpose enumerator over many types. The tradeoff for this generalization is speed, and if you rely heavily on string iteration you should use a For loop instead. Since strings are simple character arrays, they can be walked using much less overhead than other structures. The JIT is smart enough (in many cases) to optimize away bounds-checking and other things inside a For loop, but is prohibited from doing this on foreach walks. The end result is that in version 1, a For loop on strings is up to five times faster than using foreach. This will change in future versions, but for version 1 this is a definite way to increase performance.

Smile 

 


Apurva Kaushal
0
apurva
1/23/2008 9:10:35 AM

When using a for Loop, if you wish to remove an item from the collection you are iterating through it can be done very easily. When using foreach you will get an exception stating that the item cannot be removed. This can be a real gotcha so keep your eyes open for it :)


Please mark the most helpful reply/replies as "Answer".
0
anonymouse
1/23/2008 9:18:03 AM

always use "for" when u know the counter range

and use  

"foreach" when u need to iterate through the collection which has implemented ienumerable

for more details go on following links: 

blogs.msdn.com/brada/archive/2004/04/29/123105.aspx

geekswithblogs.net/flanakin/archive/2004/02/10/2002.aspx


Always "Mark an Answer" to all those posts which gave you solution so other people could know the solutions.

Muhammad Adnan
.Net Evangelist
http://weblogs.asp.net/muhammadadnan
http://realfantasy.wordpress.com
0
realfantasy
1/23/2008 9:42:11 AM

If you are going with array collection of known collection with controls and gridview, arraylist etc., then going with foreach is best. if you need to check any other condition before entering into loop then going for "for( )" is best.
 

MulukutlaCool 

0
Mulukutla
1/23/2008 9:53:51 AM

Foreach statement is used in an array or an object collection. The foreach statement is used to iterate through the collection to get the desired information.

For loop can be used in simple itearion over an array until the desired condition is reached.

So i feel for simple itearions you can use for loops and iteration through the collection objects you can use foreach..

The difference lies depends on your requirement

 

Regards

Nicsam


Regards
Nicsam

[!!!!!!!Hopes this helps you!!!!!!!]





0
Nicsam
1/23/2008 10:22:57 AM

FOR:

for (int i = 0; i < namesArrayList.Count; i++)    {        Response.Write(namesArray[i] + "...<br>");

    }

 

This is just one of many problems with using a for loop.  You always have to "know" the count/length.  You have to know if it's a 0 or 1 based array, etc.   In this case we're working with strings, so it's pretty straightforward, but things also get more complicated when working with complex object types since we have to explicitly convert each object before we can use it.

 

 FOREACH: foreach (string name in namesArray)    {        Response.Write(name + "...<br>");   

 }

 There are a few things that should be pointed out about this code as compared with the for syntax. 1.      You don't have to know the bounds/dimentions of the array  

2.      It automatically gives you an instance (of the right type) of whatever is collected by the array (a string in this case). 

3.      The syntax (and therefore the resulting code) is just so much cleaner

4.      This same syntax will work whether you're iterating over an array, ArrayListHashtable or any other type of collection.

 

In this Case Foreach gives better Performance. 

 

0
Sandhyap
1/23/2008 10:27:14 AM

 sorry for asking about "namesArrayList.Count"

will it spend time to get the Count value? or don't?

thank you 

 

I just think

for ( int i =0 ; i<namesArrayList.Count ;i++)   → does it mean program need to spend time to go through all items just for get the "Count" value?

if it will spend time to get Count

does it mean use foreach will more efficient than use for?

 thanks
 

0
jcjcjc
1/23/2008 11:17:09 AM

For  is the best enumerator in that scenario.

MulukutlaCool 

0
Mulukutla
1/23/2008 12:02:40 PM

foreach looppracticly used with controls e.g you have gridview with check boxes and admin have rights to delete more than one record from grid view. you can used foreach to iterate through each row of gridview


http://www.munishbhatia.com
0
munishbhatia
1/25/2008 11:09:14 PM
Reply:

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