for loop in c sharp.net

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I have this code. I want all the number are printed out on textbox, but there is only the last number is printed.

C#

private void btnDeal_Click(object sender, EventArgs e)
        {
            
            int[] numbers = { 9, 8, 7, 6 };
            for (int i = 0; i != numbers.Length; i++)
            {                
                int num = numbers[i];
                txtNorth.Text = num.ToString();
                i++;
            }

        }

How to print all number to textbox.

thanks,

Posted 2-Nov-11 11:22am

chaupha

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Sergey Alexandrovich Kryukov · Answer 1 · 2011-11-02T13:54:00

OK, let's point out all bugs:

C#

private void btnDeal_Click(object sender, EventArgs e) //not a bug but violation of naming conventions
        {
            int[] numbers = { 9, 8, 7, 6 }; //hard-coded
            //no need to use for cycler, foreach is simpler, and i is not needed
            for (int i = 0; i != numbers.Length; i++) //bad variable name, use < numbers.Length instead
            {                
                int num = numbers[i]; 
                txtNorth.Text = num.ToString(); //data from old iterations is lost
                i++; //incremented again; don't operate cycle variable!
            } 
}

Fixed:

C#

static readonly int[] numbers = { 9, 8, 7, 6 };
static string delimiter = " "; //never use immediate constants, only use explicit constants

//..

btnDeal.Click += (sender, eventArgs) => { //anonymous delegate is the best
    System.Text.StringBuilder sb = new System.Text.StringBuilder();
    foreach(int number in numbers) {
        sb.Append(number.ToString());
        sb.Append(delimiter);
    }
    txtNorth.Text = sb.ToString().Trim(); //trim to remove last delimiter
} //btnDeal.Click

This is a variant of delegate method for C# v.2 where lambda syntax was not yet introduced:

C#

btnDeal.Click += delegate(object sender, System.EventArgs eventArgs) { //explicitly declared types needed
    //... same as above
}
</pre>

Some explanation about Microsoft naming conventions: Yes, this name was generated by Microsoft, by Designer. So what? Who told that you're supposed to leave these names as is? You should renamed all auto-generated names into semantic names. The refactoring engine makes it easy. Do it, if you want to get maintainable code. I would recommend not creating event handlers with Designer at all (as I did above), but many don't like it. OK, but at least use semantic names.

Also, it makes no sense to show same thing on button click, potentially again and again, but I hope this is just for study of other techniques.

Good luck,

—SA

Usman Mahmood · Answer 2 · 2011-11-02T12:14:00

The problem is with assigning string to text box.
In current code when for loop iterates it will assign a new value from integer array to text box and old value is overwritten as is a reason for showing only last element of array. Also remove extra i++ statement at the end of code.

C#

private void btnDeal_Click(object sender, EventArgs e)
        {

            int[] numbers = { 9, 8, 7, 6 };
            for (int i = 0; i < numbers.Length; i++)
            {
                int num = numbers[i];
                txtNorth.Text += num.ToString() + " ";
            }

        }

Hope this help in rectifying error.

lewax00 · Answer 3 · 2011-11-02T12:05:00

Solution 3

This code:

C#

txtNorth.Text = num.ToString();

overwrites the contents of the text each time the loop is called. You want something like:

C#

txtNorth.Text += num.ToString() + Environment.NewLine;

(assuming of course you want them all on different lines, if not replace Environment.NewLine with your desired separator).

Also, calling i++ at the end of the loop is unnecessary, the loop already does that (which is why the "for (int i = 0; i != numbers.Length; i++)" has i++ in it already)

Posted 2-Nov-11 12:05pm

lewax00

Updated 2-Nov-11 12:10pm

v3

Comments

Sergey Alexandrovich Kryukov 2-Nov-11 19:41pm

I just had to vote 3 for use of "+=" for string in cycle, which is the incredible well-known performance "bug". Do you know that strings are immutable, so in each operation you get more and more data copied back and forth. In this example, you should use System.Text.StringBuilder, never "+=".
--SA

lewax00 2-Nov-11 23:13pm

I don't think the performance really matters for an array of 4 values. I'm just trying to keep it as simple as possible for the asker.

Harsha143 · Answer 4 · 2011-11-02T12:04:00

Solution 2

Hello,
Everything is fine there but u r checking with wrong condition..

use <= instead of !=

Posted 2-Nov-11 12:04pm

Harsha143

Comments

lewax00 2-Nov-11 18:08pm

<= would call one beyond the bounds of the array. < would be fine, but != works as well, assuming you increment by 1 each time.

Sergey Alexandrovich Kryukov 2-Nov-11 19:42pm

Really bad answer.
--SA