Develop Reference

Textbox to Label errors in C#

I am building a WinForm in C# and have no clue what I am doing. I have made it this far and this section is working but after entering numbers into the textbox and then removing them to change them I get an "Input string was not correct format" error. I am pretty sure this is because it is returning to a blank state and have tried putting an If statement in but keep getting errors on that because of Int or String type. How can I handle this and I am sure this is not the easiest or best way to do it but its how I got this working so far.
Thanks,
private void txt_RP7_TextChanged(object sender, EventArgs e)
{
int rw = Convert.ToInt32(txt_WeightRemain.Text);
int ld = Convert.ToInt32(txt_LayerD.Text);
int pl = rw * ld / 100;
int rp = Convert.ToInt32(txt_RP7.Text);
int rwr = pl * rp / 100;
string rwrs = rwr.ToString();
lbl_RW7.Text = rwrs ;
}

Use TryParse when dealing with input from users that may be invalid entries.
if (int.TryParse(txt_WeightRemain.Text, out var rw))
{
// valid int
}
else
{
// does not represent an int
}

Try to not use Convert. Try using
int.TryParse(txt_WeightRemain.text, out int rw)
int _rw = rw
Why? Because with that, if the text box is empty it will give you 0 for the value, not null or empty string.
When using convert and the value is empty then it will give such an error.
And try to make your code more safe to avoid the divison by zero error. Basic math for that.
Sorry for my bad english, just trying to help.

Specifying the length of Int containing 0s

I want to convert a string which contains 5 zeros ("00000") into a Int so it can be incremented.
Whenever I convert the string to an integer using Convert.ToInt32(), the value becomes 0.
How can I ensure that the integer stays at a fixed length once converted?
I want to be able to increment the value from "00000" to "00001" and so on so that the value appears with that many digits in a database instead of 0 or 1.
If you are going to down vote question, the least you could do is leave feedback on why you did it...

An integer is an integer. Nothing more.
So the int you have has value zero, there is no way to add any "length" metadata or similar.
I guess what you actually want is, that - at some point - there will be a string again. You want that string to represent your number, but with 5 characters and leading zeroes.
You can achieve that using:
string s = i.ToString("00000")
EDIT
You say you want the numbers to appear like that in your DB.
Ask yourself:
Does it really need to be like that in the DB or is it sufficient to format the numbers as soon as you read them from the database?
Depending on that, format them (as shown above), either when writing to or reading from the DB. Of course, the former case will require more storage space and you cannot really use SQL or similar to perform arithmetic operations!

An integer doesn't have a length, it's purely a numerical value. If you want to keep the length, you have to store the information about the length somewhere else.
You can wrap the value in an object that keeps the length in a property. Example:
public class FormattedInt {
private int _value, _length;
public FormattedInt(string source) {
_length = source.Length;
_value = Int32.Parse(source);
}
public void Increase() {
_value++;
}
public override string ToString() {
return _value.ToString(new String('0', _length));
}
}
Usage:
FormattedInt i = new FormattedInt("0004");
i.Increase();
string s = i.ToString(); // 0005

As olydis says above, an int is just a number. It doesn't specify the display format. I don't recommend storing it padded out with zeroes in a database either. It's an int, store it as an int.
For display purposes, in the app, a report, whatever, then pad out the zeroes.
string s = i.ToString("00000");

Input string was not in a correct format. Converting string to int

Input string was not in correct form.
I'm getting an exception on runtime as "System.FormatException".
Follwing lines shows exception-
public int Task
{
get
{
return Int32.Parse(TaskText.Text);
}
set
{
TaskText.Text = value.ToString();
}
}
public int Project
{
get
{
return Int32.Parse(ProjectText.Text);
}
set
{
ProjectText.Text = value.ToString();
}
}
I also tried -
Convert.ToInt32(TaskText.Text)
Convert.ToInt32(ProjectText.Text)
I need to pass these to following constructor,
Harvest_TimeSheetEntry entry = new Harvest_TimeSheetEntry(client,starttime,stoptime,task,project);
this constructor is stored in some class with task and project as integer parameters. And I can't change it because if i changed, it affects other code.

It looks as though you're getting your input from controls accepting user input, which is just asking for failure, since a user can potentially enter something that doesn't represent an integer value. You can use TryParse to avoid this:
var result = 0;
if (int.TryParse(TaskText.Text, out result)) {
return result;
}
return 0;
So, if the value of TaskText.Text == "1", this will succeed; if the value of TaskText.Text == "aaaa", this will fail - and return zero. You example would raise the appropriate exception, as experienced.
However, an exception might be the right thing to happen here, if you can't handle a bad value, don't have an alternative, and the application relies on the input to move forward. More likely, you could do with some validation on your input fields to prevent bad data being submitted.

Since your Harvest_TimeSheetEntry constructor expects task and project to be integers, you must have a list of integers that correspond to the different tasks and projects. Now you can't expect Int32 to know which task corresponds to which number, can you?
I would suggest you use ComboBoxes for TaskText and ProjectText. Then, you can assign the correct corresponding integer to each ComboBoxItem.Tag.
Please note that this goes far beyond the kind of answers you should expect from SO.

if you do not use MVVM or binding you can simply do the check before your need it. t
int task;
int project;
if(!Int32.TryParse(TaskText.Text, out task))
{} //errorhandling here
if(!Int32.TryParse(ProjectText.Text, out project))
{}//errorhandling here
//all fine
var entry = new Harvest_TimeSheetEntry(client,starttime,stoptime,task,project);

You must check if you can parse it into Integer
try
Int32 foo =0;
if (Int32.TryParse(TaskText.Text, out foo))
{
return foo;
}

conversion from string to int while passing as a parameter in a method

I have a method that inputs an integer as a parameter in a class -
public string OddNumbers(int input)
and in my main program, I am trying to accept an integer from the user, through a textbox, and I am converting the input string to integer while passing the parameter -
string odd = od.OddNumbers(int.Parse((TextBox1.Text))).ToString();
and I am getting the following error:
"System.FormatException: Input string was not in a correct format."
I tried different methods of converting the integer to string, but results in the same error, for example:
string odd = od.OddNumbers(Convert.ToInt32(TextBox1.Text));
Any help in pointing out where I am going wrong?

What input are you trying to enter?
I would try a couple of things.
1) Run a trim on the input before passing it into the parse command. This will make sure there are no empty spaces at the end of the number.
2) If you are trying to accept a decimal, make sure you use double.

Do not nest functions, it makes code incredibly difficult do debug and maintain.
int Number;
if (int.TryParse(TextBox1.Text, out Number) == false)
{
// parsing error
Number = -1;
}
string odd = od.OddNumbers(Number);

The following should work assuming that the user enters a valid integer in the textbox:
int i = int.Parse(TextBox1.Text);
string odd = od.OddNumbers(i).ToString();
Another possible way to handle this is to use the TryParse method:
int i;
if (int.TryParse(TextBox1.Text, out i))
{
string odd = od.OddNumbers(i).ToString();
}
else
{
MessageBox.Show(TextBox1.Text + " is not a valid integer");
}

Once i put the method inside an click event, which finds out whether the input integer is odd or even, it gave me the desired result. thanks for all the inputs.

C# Converting a string containing a floating point to an integer

What is the best way to take a string which can be empty or contain "1.2" for example, and convert it to an integer? int.TryParse fails, of course, and I don't want to use float.TryParse and then convert to int.

Solution 1: Convert.ToDouble (culture-dependent)
You may using Convert.ToDouble. But, beware! The below solution will work only when the number separator in the current culture's setting is a period character.
var a = (int)Convert.ToDouble("1.2");
Solution 2: Convert.ToDouble (culture-independent)
It's preferable to use IFormatProvider and convert the number in an independent way from the current culture settings:
var a = (int)Convert.ToDouble("1.2", CultureInfo.InvariantCulture.NumberFormat);
Solution 3: Parse & Split
Another way to accomplish this task is to use Split on parsed string:
var a = int.Parse("1.2".Split('.')[0]);
Or:
var a = int.Parse("1.2".Split('.').First());
Notes
If you want to handle empty and null strings, write a method and add string.IsNullOrEmpty condition.
To get decimal separator for the current culture setting, you can use NumberFormatInfo.NumberDecimalSeparator property.
You should also keep eye on rounding to avoid traps.
Select casting, Parse, TryParse or Convert class wisely. Read more at:
How to: Convert a string to an int (C# Programming Guide)
How to: Determine Whether a String Represents a Numeric Value (C# Programming Guide)

I don't know what's wrong with parsing to a float and converting to an int. I doubt that any other way would be more efficient but here's an attempt:
//allows empty strings and floating point values
int ParseInt(string s, bool alwaysRoundDown = false)
{
//converts null/empty strings to zero
if (string.IsNullOrEmpty(s)) return 0;
if (!s.Contains(".")) return int.Parse(s);
string parts = s.Split(".");
int i = int.Parse(parts[0]);
if (alwaysRoundDown || parts.Length==1) return i;
int digitAfterPoint = int.Parse(parts[1][0]);
return (digitAfterPoint < 5) ? i : i+1;
}
In order to globalize the code you would need to replace "." with System.Globalization.CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator.

int a = (int)Math.Round(float.Parse("0.9"));
You need to round it first unless you want 0.9f being converted to 0 instead of 1.

Maybe you can try to delete everything after floating point using string functions and then convert to int. But seriously I don't think it's better than converting to float and then to int.

I think another way of doing it would be splitting the string into pieces taking the decimal (.) as the delimiter and then parsing for the integer. Of course, I am yet to ask you if the string might contain values like "37.56 miles in 32.65 seconds" type values.
Considering there will be only one value (string or number) in the string, I can think of something in the following line:
public int64 GetInt64(string input)
{
if (string.IsNullOrEmpty(input)) return 0;
// Split string on decimal (.)
// ... This will separate all the digits.
//
string[] words = input.Split('.');
return int.Parse(words[0]);
}

You can use the Visual Basic runtime Library to accomplish this from c#.
You need to add a reference to the assembly Microsoft.VisualBasic.dll to your solution.
Then the following code will do your conversion:
using VB = Microsoft.VisualBasic.CompilerServices;
class Program
{
static void Main(string[] args)
{
int i = VB.Conversions.ToInteger("1.2");
}
}

I had this same problem and ended up using a hybrid of Mark's and Dariusz':
if (num == "")
{
num = "0.00";
}
var num1 = (float)Convert.ToDouble(num);