validate that string input is a negative number

[Guest]

Hello,

I have a data entry windows form. One of the text boxes allows the user to
enter a string. I need this text box to only allow users to type in a
negative integer value (e.g. -1, -2, -3).

Current approach:
I want to validate the user's entry during the TextChanged() event. During
the validation, I need a function that will parse the string and see if it is
a negative integer. Does anyone have suggestions on the best way to do this?
or alternative approaches from what I have entered?

 

[Alberto Poblacion]

I have a data entry windows form. One of the text boxes allows the user
to
enter a string. I need this text box to only allow users to type in a
negative integer value (e.g. -1, -2, -3).

Current approach:
I want to validate the user's entry during the TextChanged() event.
During
the validation, I need a function that will parse the string and see if it
is
a negative integer. Does anyone have suggestions on the best way to do
this?
or alternative approaches from what I have entered?

Two different suggestions:

- Use int.TryParse to see if it is an integer, and then compare with zero
to see if it's negative.
- Use a regular expression such as "-\d+".

I have not run a benchmark, but I expect the TryParse approach to perform
faster.

 

[Larry Lard]

Two different suggestions:

- Use int.TryParse to see if it is an integer, and then compare with
zero to see if it's negative.
- Use a regular expression such as "-\d+".

I have not run a benchmark, but I expect the TryParse approach to
perform faster.

Also, that regular expression would pass "-0", which isn't negative.

 

[Alberto Poblacion]

Also, that regular expression would pass "-0", which isn't negative.

Okay, let's refine it a little:

@"^-[1-9]\d*$"

 

[Mythran]

Also, that regular expression would pass "-0", which isn't negative.

Okay, let's refine it a little:

@"^-[1-9]\d*$"

lol sorry, have too:

-01 wouldn't pass the above expression pattern...

@"^-\d*[1-9]\d*$" should...haven't tested though...

Mythran

 

[mpetrotta]

Okay, let's refine it a little:

@"^-[1-9]\d*$"

lol sorry, have too:

-01 wouldn't pass the above expression pattern...

@"^-\d*[1-9]\d*$" should...haven't tested though...

Or just a nice simple
int val;
return Int32.TryParse(s, out val) && val < 0

Michael

 

[Jon Skeet [C# MVP]]

Or just a nice simple
int val;
return Int32.TryParse(s, out val) && val < 0

Exactly. This thread is a good example of why it's wise to avoid using
regular expressions where they're not truly advantageous