C#•2y ago

❔ Item.Is a Number

Hey, I have this list:

        { "+", "-", "*", "/", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" };

        { "+", "-", "*", "/", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" };

I iterate through the list with a foreach. I want to check if the item is a number or not. So is there something like

foreach
   if((int)item.Is a number)
      .....

foreach
   if((int)item.Is a number)
      .....

11 Replies

EinfachNurBaumOP•2y ago

or something similar, that don't causes a error

Angius•2y ago

$tryparse

MODiX•2y ago

The TryParse pattern is considered best practice of parsing data from a string: - a TryParse method returns true or false to inform you if it succeeded or not, so you can use it directly in a condition, - since C# 7 you can declare a variable that will be used as an out argument inline in an argument list, - it forces you to check if the out argument contains valid data afterwards, Avoid: Convert.ToInt32 — it's a bad choice for parsing an int. It exists only for backwards compatibility reasons and should be considered last resort.

return Convert.ToInt32(null); //returns 0. null should not be considered as 0 ever
return Convert.ToInt32("asdf"); //throws FormatException

return Convert.ToInt32(null); //returns 0. null should not be considered as 0 ever
return Convert.ToInt32("asdf"); //throws FormatException

(Note: Convert does contain useful conversion methods: To/FromBase64String, To/FromHexString, ToString(X value, int toBase), ToX(string? value, int fromBase)) Avoid: int.Parse — you have to use a try/catch statement to handle invalid input, which is a less clean solution.

var number = int.Parse("abc"); //throws FormatException
var number = int.Parse(""); //throws FormatException

var number = int.Parse("abc"); //throws FormatException
var number = int.Parse(""); //throws FormatException

Use int.TryParse https://docs.microsoft.com/en-us/dotnet/api/system.int32.tryparse?view=net-5.0#System_Int32_TryParse_System_String_System_Int32__

if (int.TryParse(someInput, out var result))
{
  Console.WriteLine($"Thanks for giving me the following number: {result}!");
}
else
{
  Console.WriteLine("You didn't give me a valid number :c");
}

if (int.TryParse(someInput, out var result))
{
  Console.WriteLine($"Thanks for giving me the following number: {result}!");
}
else
{
  Console.WriteLine("You didn't give me a valid number :c");
}

Int32.TryParse Method (System)

Converts the string representation of a number to its 32-bit signed integer equivalent. A return value indicates whether the operation succeeded.

Angius•2y ago

Or char.IsNumber() IIRC

.logik.•2y ago

Maybe you're looking for the Char.IsDigit static method?

Angius•2y ago

Ah, yeah, this one, not .IsNumber()

EinfachNurBaumOP•2y ago

Thanks $close

ero•2y ago

yeah but they're not chars right

Angius•2y ago

Just [0] them then Or use int.TryParse()

EinfachNurBaumOP•2y ago

I have never used chars and int.tryParse() is the thing that matchs better

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Item.Is a Number