Putting restrictions on if statements

Question

This is a very basic question but how do i only allow numberic values in my if statement? For example if user inputs string as an id it should give an error saying only numeric value allowed.

Console.Write("Please enter your ID: ");
int id = Int32.Parse(Console.ReadLine());
if () // what should I write here?
{
    Console.WriteLine("Only Numeric value are allowed.");
}else{
Console.WriteLine("My ID is {0}", id);}

can you use the `char.IsDigit` function perhaps ..? read up on it and try it.. — MethodMan, Sep 15 '14 at 15:13
you could just not have the if sentence at all. Int32.Parse will throw an exception if the string is not a valid number.. so `try{ int id = Int32.Parse(Console.ReadLine()); Console.WriteLine("My ID is {0}", id);} }catch{ Console.WriteLine("Only Numeric value are allowed."); }` is an option.. — Henrik, Mar 27 '18 at 09:17

Habib · Accepted Answer · 2014-09-15T15:27:24.013

6

Use int.TryParse

Console.Write("Please enter your ID: ");
int id;
if (!int.TryParse(Console.ReadLine(), out id)) // what should I write here?
{
    Console.WriteLine("Only Numeric value are allowed.");
}
else
{
    Console.WriteLine("My ID is {0}", id);
}

TryParse group of methods will not raise an exception if parsing is failed, instead they returns a bool indicating success or failure.

edited Sep 15 '14 at 15:27

answered Sep 15 '14 at 15:13

Habib

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It's giving an error saying "the best overloaded method have some invalid argument". :/ – djinc Sep 15 '14 at 15:26
1

@samjohal, my bad, it should have been `Console.ReadLine`, instead of `Console.Read` – Habib Sep 15 '14 at 15:27

score 3 · Answer 2 · answered Sep 15 '14 at 15:14

3

You should do the parse in the if using int.TryParse:

int id;

if (Int32.TryParse(Console.ReadLine(), out id))
{
    // it's an integer!
}
else
{
}

answered Sep 15 '14 at 15:14

Patrick Hofman

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score 0 · Answer 3 · edited Sep 15 '14 at 15:15

0

You could use a regular expression such as:

if(Regex.IsMatch("[0-9]") == false)

edited Sep 15 '14 at 15:15

Patrick Hofman

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answered Sep 15 '14 at 15:14

Steven Wood

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Not the preferred approach, since you need to parse it twice. `int.TryParse` does it all for you. – Patrick Hofman Sep 15 '14 at 15:15

Putting restrictions on if statements

3 Answers3