Develop Reference

Simple Calculator, System.FormatException

I'm trying to make a simple calculator and its fully working but when I calculate without a = button, my program completely crashes and gives the error:
System.FormatException: 'Input string was not in correct format.'
This is the code that it throws an error to:
second = double.Parse(aNumber);
// the strings and doubles:
String aNumber = "";
double first = 0.0;

b will be true or false if the try parse worked
d will contain the double or 0 if it fails
change anum to a valid number to test.
String anum = "";
double d = 0.0;
bool b = double.TryParse(anum, out d);

double.Parse will throw an exception if the input is not valid. So you either need to use try catch - or the preferred way would be to use double.TryParse as below. The value of y below will be set to the value if TryParse returns true.
class Program
{
static void Main(string[] args)
{
// This will cause an exception
var someString = "SomeValue";
var x = double.Parse(someString); // Comment this line out to run this example
// This will work
double y;
if (double.TryParse(someString, out y))
{
Console.WriteLine(someString + " is a valid decimal");
}
else
{
Console.WriteLine(someString + " is not a valid decimal");
}
someString = "14.7";
if (double.TryParse(someString, out y))
{
Console.WriteLine(someString + " is a valid decimal");
}
else
{
Console.WriteLine(someString + " is not a valid decimal");
}
}
}

string to decimal using extension methods

My string is 1799.00
I want to like this: 1.799,00
But i cannot convert this method.
I'm using this function.
public static decimal ToDecimal(this object str)
{
if (str != null)
{
try
{
return Convert.ToDecimal(str, new CultureInfo("tr-TR"));
}
catch (Exception)
{
return 0;
}
}
else
{
return 0;
}
}

You are, probably, looking for changing formats. Given a decimal as a string in invariant culture representation ("1799.00") you want a string, but in Turkish cutrure representation: ("1.799,00")
// you want to return string in Turkish culture, right?
public static string ToTuskishDecimal(this object value) {
if (null == value)
return null; // or throw exception, or return "0,00" or return "?"
try {
return Convert
.ToDecimal(value, CultureInfo.InvariantCulture)
.ToString("N", CultureInfo.GetCultureInfo("tr-TR"));
}
catch (FormatException) {
return "0,00"; // or "?"
}
}
Test:
decimal d = 1799.00m;
string s = d.ToString(CultureInfo.InvariantCulture);
// 1.799,00
Console.Write(d.ToTuskishDecimal());
// 1.799,00
Console.Write(s.ToTuskishDecimal());
In case you want to return decimal you have to format it manually when printing out:
public static decimal ToDecimal(this object value) {
if (null == value)
return 0.00m;
try {
return Convert.ToDecimal(value, CultureInfo.InvariantCulture);
}
catch (FormatException) {
return 0.00m;
}
}
...
// return me a decimal, please
decimal d = "1799.00".ToDecimal();
// when printing decimal, use Turkish culture
Console.Write(d.ToString("N", CultureInfo.GetCultureInfo("tr-TR")));
you can specify Turkish culture as a default one for the entire thread:
Thread.CurrentThread.CurrentCulture = CultureInfo.GetCultureInfo("tr-TR");
...
// now you don't have to mention Turkish culture
// ...but still have to specify the format
Console.Write(d.ToString("N"));

I use this to obtain a decimal value:
public static decimal toDecimal( string s ) {
decimal res = 0;
decimal.TryParse(s.Replace('.', ','), out res);
return res;
}
In case you want to show the decimal value on the format you ask, try this:
toDecimal("1700.99").ToString("N2")
you will obtain the "1.700,99" string.

I wrote another simple example to obtain a decimal value in Turkish format:
decimal value = 1700.00m;
Console.WriteLine(value.ToString("N", CultureInfo.GetCultureInfo("tr-TR")));

Avoid round off decimals in Datagridview control

In the Datagridview I have a column "C" which is product of Column "A" and "B".
Example
Column A Value - 8.14
Column B Value - 0.2
Now the column C value is 12.296 and after decimal I want to show first two numbers like
12.29 without rounding to 12.30.
Below is the code i used to achieve the above result.
public class CustomFormatter : IFormatProvider, ICustomFormatter
{
public object GetFormat(Type formatType)
{
if (formatType == typeof(ICustomFormatter))
return this;
else
return null;
}
public string Format(string format, object arg, IFormatProvider formatProvider)
{
// Check whether this is an appropriate callback
if (!this.Equals(formatProvider))
return null;
if (arg == null) return null;
string numericString = arg.ToString();
decimal result = 0;
if (Decimal.TryParse(numericString, out result))
{
return ((Math.Truncate(result * 100)) / 100).ToString();
}
else
{
return null;
}
}
}
private void gvItemDetails_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
{
try
{
if (e.ColumnIndex == gvItemDetails.Columns["Vat Amount"].Index)
{
gvItemDetails[e.ColumnIndex, e.RowIndex].Value = String.Format(new CustomFormatter(), "{0}", e.Value);
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
When i put a break point on cellformatting code..i can see the code is repeated continously but not returning any stackoverflow exception. When i remove the breakpoint its working.
Can you please advice what might be the problem or suggest any other alternative to prevent it from rounding an show 12.29 not 12.30.
Thanks,
Prathap.

First, i tried to use the same method which you used. It works perfectly fine for me and produces desired "12.29".
string numericString = "12.2963";
string truncatedString = string.Empty;
decimal result = 0;
if (Decimal.TryParse(numericString, out result))
{
truncatedString = ((Math.Truncate(result * 100)) / 100).ToString();
}
In case, above method doesn't work for you, another simple alternative would be to use string.substring (this will be useful only when intermediate decimal value is not required for you).
string numericString = "12.2963";
string truncatedString = string.Empty;value
int endIndex = numericString.IndexOf('.');
truncatedString = numericString.Substring(0, endIndex + 3);
Update:
Though i haven't tested it, you should be able to define format provider this way :
this.dataGridView1.Columns["XYZ"].DefaultCellStyle.FormatProvider = new CustomFormatter();
and for format (here format string will have pre-defined meaning) :
this.dataGridView1.Columns["XYZ"].DefaultCellStyle.Format = "c";
Update 2:
Unfortunately, even if you are using FormatProvider, you still need to handle cellformatting event; Check This.
Good news is that you don't need to use FormatProvider for this. Try following format, it should work for you:
this.dataGridView1.Columns["XYZ"].DefaultCellStyle.Format = "0.##";

C# How to format a double to one decimal place without rounding

I need to format a double value to one decimal place without it rounding.
double value = 3.984568438706
string result = "";
What I have tried is:
1)
result = value.ToString("##.##", System.Globalization.CultureInfo.InvariantCulture) + "%";
// returns 3.98%
2)
result = value.ToString("##.#", System.Globalization.CultureInfo.InvariantCulture) + "%";
// returns 4%
3)
result = value.ToString("##.0", System.Globalization.CultureInfo.InvariantCulture) + "%";
// returns 4.0%
4) (Following other suggestions)
value = (value / 100);
result = String.Format("{0:P1}", Math.Truncate(value * 10000) / 10000);
// returns 4.0%
result = string.Format("{0:0.0%}",value); // returns 4.0%
What I need to display is the value 3.9%
Thanks for any help in advance.

result=string.Format("{0:0.0}",Math.Truncate(value*10)/10);

I would make a utility method to handle this:
static double Truncate(double value, int digits)
{
double mult = System.Math.Pow(10.0, digits);
return System.Math.Truncate(value * mult) / mult;
}
You could then do:
result = Truncate(value, 1).ToString("##.#", System.Globalization.CultureInfo.InvariantCulture) + "%";
Note that you may also want Math.Floor instead of truncate - but it depends on how you want negative values handled.

I know this is a old thread but I've just had to do this. While the approaches here work I want a easy way to be able to affect a lot of calls so using the Math.Truncate on all the calls to string.format wasn't really a good option.
Thus, I made a custom format provider which would allow me to add truncation to the formatting string, eg
string.format(new FormatProvider(), "{0:T}", 1.1299); // 1.12
string.format(new FormatProvider(), "{0:T(3)", 1.12399); // 1.123
string.format(new FormatProvider(), "{0:T(1)0,000.0", 1000.9999); // 1,000.9
The implementation is pretty simple and is easily extendible to other requirements.
public class FormatProvider : IFormatProvider, ICustomFormatter
{
public object GetFormat(Type formatType)
{
if (formatType == typeof (ICustomFormatter))
{
return this;
}
return null;
}
public string Format(string format, object arg, IFormatProvider formatProvider)
{
if (arg.GetType() != typeof (double))
{
try
{
return HandleOtherFormats(format, arg);
}
catch (FormatException e)
{
throw new FormatException(string.Format("The format of '{0}' is invalid.", format));
}
}
if (format.StartsWith("T"))
{
int dp = 2;
int idx = 1;
if (format.Length > 1)
{
if (format[1] == '(')
{
int closeIdx = format.IndexOf(')');
if (closeIdx > 0)
{
if (int.TryParse(format.Substring(2, closeIdx - 2), out dp))
{
idx = closeIdx + 1;
}
}
else
{
throw new FormatException(string.Format("The format of '{0}' is invalid.", format));
}
}
}
double mult = Math.Pow(10, dp);
arg = Math.Truncate((double)arg * mult) / mult;
format = format.Substring(idx);
}
try
{
return HandleOtherFormats(format, arg);
}
catch (FormatException e)
{
throw new FormatException(string.Format("The format of '{0}' is invalid.", format));
}
}
private string HandleOtherFormats(string format, object arg)
{
if (arg is IFormattable)
{
return ((IFormattable) arg).ToString(format, CultureInfo.CurrentCulture);
}
return arg != null ? arg.ToString() : String.Empty;
}
}

ToString() doesn't do it. You have to add extra code. The other answers show math approaches, my approach below is kind of outside-the-box.
string result = value.ToString();
Console.WriteLine("{0}", result.Substring(0, result.LastIndexOf('.') + 2));
This is a fairly simple brute force approach, but it does the trick when the decimal is a '.'. Here's an extension method to ease the pain (and deals with the decimal point).
public static class Extensions
{
public static string ToStringNoTruncate(this double me, int decimalplaces = 1)
{
string result = me.ToString();
char dec = System.Globalization.CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator[0];
return result.Substring(0, result.LastIndexOf(dec) + decimalplaces + 1);
}
}

( Math.Truncate( ( value * 10 ) ) / 1000 ).ToString( "#.#%" )

Just use modulo operator + built in ToString:
result = (value - (value % 0.1)).ToString("N1") + "%";

How can I check if a string is a number?

I'd like to know on C# how to check if a string is a number (and just a number).
Example :
141241 Yes
232a23 No
12412a No
and so on...
Is there a specific function?

Look up double.TryParse() if you're talking about numbers like 1, -2 and 3.14159. Some others are suggesting int.TryParse(), but that will fail on decimals.
string candidate = "3.14159";
if (double.TryParse(candidate, out var parsedNumber))
{
// parsedNumber is a valid number!
}
EDIT: As Lukasz points out below, we should be mindful of the thread culture when parsing numbers with a decimal separator, i.e. do this to be safe:
double.TryParse(candidate, NumberStyles.AllowDecimalPoint, CultureInfo.InvariantCulture, out var parsedNumber)

If you just want to check if a string is all digits (without being within a particular number range) you can use:
string test = "123";
bool allDigits = test.All(char.IsDigit);

Yes there is
int temp;
int.TryParse("141241", out temp) = true
int.TryParse("232a23", out temp) = false
int.TryParse("12412a", out temp) = false
Hope this helps.

Use Int32.TryParse()
int num;
bool isNum = Int32.TryParse("[string to test]", out num);
if (isNum)
{
//Is a Number
}
else
{
//Not a number
}
MSDN Reference

Use int.TryParse():
string input = "141241";
int ouput;
bool result = int.TryParse(input, out output);
result will be true if it was.

Yep - you can use the Visual Basic one in C#.It's all .NET; the VB functions IsNumeric, IsDate, etc are actually static methods of the Information class. So here's your code:
using Microsoft.VisualBasic;
...
Information.IsNumeric( object );

int value;
if (int.TryParse("your string", out value))
{
Console.WriteLine(value);
}

This is my personal favorite
private static bool IsItOnlyNumbers(string searchString)
{
return !String.IsNullOrEmpty(searchString) && searchString.All(char.IsDigit);
}

Perhaps you're looking for the int.TryParse function.
http://msdn.microsoft.com/en-us/library/system.int32.tryparse.aspx

Many datatypes have a TryParse-method that will return true if it managed to successfully convert to that specific type, with the parsed value as an out-parameter.
In your case these might be of interest:
http://msdn.microsoft.com/en-us/library/system.int32.tryparse.aspx
http://msdn.microsoft.com/en-us/library/system.decimal.tryparse.aspx

int result = 0;
bool isValidInt = int.TryParse("1234", out result);
//isValidInt should be true
//result is the integer 1234
Of course, you can check against other number types, like decimal or double.

You should use the TryParse method for the int
string text1 = "x";
int num1;
bool res = int.TryParse(text1, out num1);
if (res == false)
{
// String is not a number.
}

If you want to validate if each character is a digit and also return the character that is not a digit as part of the error message validation, then you can loop through each char.
string num = "123x";
foreach (char c in num.ToArray())
{
if (!Char.IsDigit(c))
{
Console.WriteLine("character " + c + " is not a number");
return;
}
}

int.TryPasrse() Methode is the best way
so if the value was string you will never have an exception , instead of the TryParse Methode return to you bool value so you will know if the parse operation succeeded or failed
string yourText = "2";
int num;
bool res = int.TryParse(yourText, out num);
if (res == true)
{
// the operation succeeded and you got the number in num parameter
}
else
{
// the operation failed
}

string str = "123";
int i = Int.Parse(str);
If str is a valid integer string then it will be converted to integer and stored in i other wise Exception occur.

Starting with C# 7.0, you can declare the out variable in the argument
list of the method call, rather than in a separate variable
declaration. This produces more compact, readable code, and also
prevents you from inadvertently assigning a value to the variable
before the method call.
bool isDouble = double.TryParse(yourString, out double result);
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/out-parameter-modifier

You could use something like the following code:
string numbers = "numbers you want to check";
Regex regex = new Regex("^[0-9]+$"));
if (regex.IsMatch(numbers))
{
//string value is a number
}

public static void Main()
{
string id = "141241";
string id1 = "232a23";
string id2 = "12412a";
validation( id, id1, id2);
}
public static void validation(params object[] list)
{
string s = "";
int result;
string _Msg = "";
for (int i = 0; i < list.Length; i++)
{
s = (list[i].ToString());
if (string.IsNullOrEmpty(s))
{
_Msg = "Please Enter the value";
}
if (int.TryParse(s, out result))
{
_Msg = "Enter " + s.ToString() + ", value is Integer";
}
else
{
_Msg = "This is not Integer value ";
}
}
}

Try This
here i perform addition of no and concatenation of string
private void button1_Click(object sender, EventArgs e)
{
bool chk,chk1;
int chkq;
chk = int.TryParse(textBox1.Text, out chkq);
chk1 = int.TryParse(textBox2.Text, out chkq);
if (chk1 && chk)
{
double a = Convert.ToDouble(textBox1.Text);
double b = Convert.ToDouble(textBox2.Text);
double c = a + b;
textBox3.Text = Convert.ToString(c);
}
else
{
string f, d,s;
f = textBox1.Text;
d = textBox2.Text;
s = f + d;
textBox3.Text = s;
}
}

I'm not a programmer of particularly high skills, but when I needed to solve this, I chose what is probably a very non-elegant solution, but it suits my needs.
private bool IsValidNumber(string _checkString, string _checkType)
{
float _checkF;
int _checkI;
bool _result = false;
switch (_checkType)
{
case "int":
_result = int.TryParse(_checkString, out _checkI);
break;
case "float":
_result = Single.TryParse(_checkString, out _checkF);
break;
}
return _result;
}
I simply call this with something like:
if (IsValidNumber("1.2", "float")) etc...
It means that I can get a simple true/false answer back during If... Then comparisons, and that was the important factor for me. If I need to check for other types, then I add a variable, and a case statement as required.

use this
double num;
string candidate = "1";
if (double.TryParse(candidate, out num))
{
// It's a number!
}

int num;
bool isNumeric = int.TryParse("123", out num);

namespace Exception
{
class Program
{
static void Main(string[] args)
{
bool isNumeric;
int n;
do
{
Console.Write("Enter a number:");
isNumeric = int.TryParse(Console.ReadLine(), out n);
} while (isNumeric == false);
Console.WriteLine("Thanks for entering number" + n);
Console.Read();
}
}
}

Regex.IsMatch(stringToBeChecked, #"^\d+$")
Regex.IsMatch("141241", #"^\d+$") // True
Regex.IsMatch("232a23", #"^\d+$") // False
Regex.IsMatch("12412a", #"^\d+$") // False

The problem with some of the suggested solutions is that they don't take into account various float number formats. The following function does it:
public bool IsNumber(String value)
{
double d;
if (string.IsNullOrWhiteSpace(value))
return false;
else
return double.TryParse(value.Trim(), System.Globalization.NumberStyles.Any,
System.Globalization.CultureInfo.InvariantCulture, out d);
}
It assumes that the various float number styles such es decimal point (English) and decima comma (German) are all allowed. If that is not the case, change the number styles paramater. Note that Any does not include hex mumbers, because the type double does not support it.