steve_mick972
asked on
Regex for match number.
I am trying to process a number. I would like to check if the number is a valid currency .
If the user enters
Input should return
--------------------------
$50000 50000
$50,000 50000
$50,000.12 50000.12
$50000.23 50000.23
USD 50,000 50000
After it matches a regex patter for currency then i use a Convert.ToDouble
Any ideas?
Thanks.
If the user enters
Input should return
--------------------------
$50000 50000
$50,000 50000
$50,000.12 50000.12
$50000.23 50000.23
USD 50,000 50000
After it matches a regex patter for currency then i use a Convert.ToDouble
Any ideas?
Thanks.
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Ceiled
As a general rule, validating numbers with regular expressions isn't a very good idea. There are a lot of issues
Shoot...sorry about that, accidentally submitted in the middle there. Let me try that again:
As a general rule, validating numbers with regular expressions isn't a very good idea. There are a lot of issues to consider, many of which are not easy to capture in a regular expression. For example, the regular expression Yurich gives above will allow strings like "1.2.3.4," which will cause Convert.ToDouble() to throw an exception, which I assume is what you're trying to avoid by doing the validation first. Instead of validating with a regular expression and then using Convert.ToDouble(), you should consider using Double.TryParse() (documented at http://msdn2.microsoft.com/library/8w0x0ctx(en-us,vs.80).aspx), which will attempt to parse a string into a double and return false if it fails, instead of throwing an exception. This is much more reliable and safer than trying to validate a number with a regular expression.
As a general rule, validating numbers with regular expressions isn't a very good idea. There are a lot of issues to consider, many of which are not easy to capture in a regular expression. For example, the regular expression Yurich gives above will allow strings like "1.2.3.4," which will cause Convert.ToDouble() to throw an exception, which I assume is what you're trying to avoid by doing the validation first. Instead of validating with a regular expression and then using Convert.ToDouble(), you should consider using Double.TryParse() (documented at http://msdn2.microsoft.com/library/8w0x0ctx(en-us,vs.80).aspx), which will attempt to parse a string into a double and return false if it fails, instead of throwing an exception. This is much more reliable and safer than trying to validate a number with a regular expression.
static double F(string S) {
string[] Currencies = new string[] { "$", "USD" };
string AuxStr = S.Trim();
double RetVal = -1;
foreach (string Currency in Currencies) {
if (AuxStr.StartsWith(Currenc
AuxStr = AuxStr.Substring(Currency.
break;
}
}
try {
RetVal = Convert.ToDouble(AuxStr);
} catch (FormatException) { }
return RetVal;
}
string[] Currencies = new string[] { "$", "USD" };
string AuxStr = S.Trim();
double RetVal = -1;
foreach (string Currency in Currencies) {
if (AuxStr.StartsWith(Currenc
AuxStr = AuxStr.Substring(Currency.
break;
}
}
try {
RetVal = Convert.ToDouble(AuxStr);
} catch (FormatException) { }
return RetVal;
}
Really no way!
How can you accept a solution that admits an aberration such as ".,3.$,5$.9,$0.$," as valid input?
That solution doesn't do ANY validity check on the format of the input as a unit. It merely restricts the valid input characters, but imposes no structure or order to them. There isn't even any numeric conversion done, so the final output for the string I quoted above gives a result of ".3.5.90.". Now what's that good for?
Also, wasn't it a requirement that the function returned 50000 for 'USD 50,000'?
How can you accept a solution that admits an aberration such as ".,3.$,5$.9,$0.$," as valid input?
That solution doesn't do ANY validity check on the format of the input as a unit. It merely restricts the valid input characters, but imposes no structure or order to them. There isn't even any numeric conversion done, so the final output for the string I quoted above gives a result of ".3.5.90.". Now what's that good for?
Also, wasn't it a requirement that the function returned 50000 for 'USD 50,000'?