C# For Loop not iterating correctly

Question

I have a 4 byte value that I convert to an Int32 and then display it in a textbox. No problems there. The problem comes in when I try padding the string with 0's. When I display the decimal number it should always contain 8 characters, so if its less than that I want to pad it with 0's.

string parmDecString = BitConverter.ToInt32(testNum, 0).ToString();
Console.WriteLine("length: {0} - {1}", parmDecString.Length, (8 - parmDecString.Length));
for (int l=0; l < (8-parmDecString.Length); l++)
{
    parmDecString = "0" + parmDecString;
}
textBox74.Text = parmDecString;

Here's the output in the textbox I get based on different 'parmDecString' values:

parmDecString = "123"
Console:  length: 3 - 5
textbox:  000123   <=== only 3 times in the 'for' loop, expected 5x

parmDecString = "12345"
Console:  length: 5 - 3
textbox:  0012345   <=== only 2 times in the 'for' loop, expected 3x

parmDecString = "12345678"
Console:  length: 8 - 0
textbox:  12345678   <=== as expected

Or, just use PadLeft https://msdn.microsoft.com/en-us/library/92h5dc07(v=vs.110).aspx — hatchet - done with SOverflow, Feb 27 '17 at 23:09
See [this question](http://stackoverflow.com/questions/4325267/c-sharp-convert-int-to-string-with-padding-zeros). — Ivan Gritsenko, Feb 27 '17 at 23:09

score 6 · Answer 1 · answered Feb 27 '17 at 23:08

First off, the right answer to this is just use the provided format strings. In your case, if you stored the number as paramDec you would use paramDec.ToString("D8"); for an 8-digit integer string representation.

The reason your for loop isn't working is that you are iterating until you reach 8 - paramDecString.Length but that length keeps changing as you append 0s. It would work if you stored the value off first:

int numZeroes = (8-parmDecString.Length); 
for (int l=0; l < numZeroes; l++)
{
    parmDecString = "0" + parmDecString;
}

Also, string appending like that is expensive. Consider using StringBuilder instead as it doesn't create a new string every time you append to it.

Thanks. I'm new to C#, so I had no idea I could even use the 8-digit integer string representation. I changed the code to use that and its working exactly as expected. This is greatly appreciated... I'll store this away so I don't make the same stupid mistake next time. — milnuts, Feb 28 '17 at 13:27

score 2 · Accepted Answer · answered Feb 27 '17 at 23:08

2

parmDecString.Length increases at every loop, try to assign it to a variable before beginning the iteration

answered Feb 27 '17 at 23:08

MatteoSp

2,940
5
28
36

score 2 · Answer 3 · answered Feb 27 '17 at 23:11

2

So you screwed up your loop by changing the bounds of the loop from within the loop... but really the loop wasn't necessary in the first place:

"123".PadLeft(8,'0') //ftw

answered Feb 27 '17 at 23:11

spender

117,338
33
229
351

score 0 · Answer 4 · answered Feb 27 '17 at 23:08

0

Change:

for (int l=0; l < (8-parmDecString.Length); l++)

with:

int limit = 8-parmDecString.Length;
for (int l=0; l < (OriginalLength); l++)

That way changing length of string will not affect your loop.

answered Feb 27 '17 at 23:08

Shadowed

956
7
19

C# For Loop not iterating correctly

4 Answers4