Using regex to check if a string contains only one digit

Question

I'm writing an algorithm and I need to check if a string contains only one digit (no more than one). Currently I have:

if(current_Operation.matches("\\d")){
...
}

Is there a better way to go about doing this? Thanks.

It seems that I am not getting the correct result with this way. Let me double check — pmcg521
– pmcg521, Commented Sep 30, 2016 at 19:49
if a string contains anywhere? I'd be tempted to just write if(str.length == 1 && isDigit(str[0]). isDigit from std.ascii is good enough for a basic check. — Adam D. Ruppe
– Adam D. Ruppe, Commented Sep 30, 2016 at 19:50
Note that the "d" tag is used for the D programming language, please refrain from using it just because you happen to have a "d" in your example — cym13
– cym13, Commented Sep 30, 2016 at 19:56

Jan · Accepted Answer · 2016-09-30 19:50:20Z

8

You can use:

^\\D*\\d\\D*$
# match beginning of the line
# non digits - \D*
# one digit - \d
# non digits - \D*
# end of the line $

See a demo on regex101.com (added newlines for clarity).

answered Sep 30, 2016 at 19:50

Jan

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1 Comment

user1999397 Over a year ago

@Jan In the same regex how can we check if digits are between 0-6 only

Andy Turner · Accepted Answer · 2016-09-30 19:57:16Z

1

If you fancied not using a regular expression:

int numDigits = 0;
for (int i = 0; i < current_Operation.length() && numDigits < 2; ++i) {
  if (Character.isDigit(currentOperation.charAt(i))) {
    ++numDigits;
  }
}
return numDigits == 1;

answered Sep 30, 2016 at 19:57

Andy Turner

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Comments

Chloe · Accepted Answer · 2016-09-30 19:49:17Z

-1

Use the regular expression

/^\d$/

This will ensure the entire string contains a single digit. The ^ matches the beginning of the line, and the $ matches the end of the line.

answered Sep 30, 2016 at 19:49

Chloe

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2 Comments

WebFreak001 Over a year ago

he asked for checking if the string contains a digit and is not only a digit. But it should only contain exactly one digit

pmcg521 Over a year ago

@WebFreak001 yes, you are correct. The string itself contains parentheses also, but I am checking if it contains only one digit.

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