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I want a regular expression to match a string that may or may not start with plus symbol and then contain any number of digits.
Those should be matched
+35423452354554 or 3423564564 
950
Occurrence Indicators (or Repetition Operators): +: one or more ( 1+ ), e.g., [0-9]+ matches one or more digits such as '123' , '000' . *: zero or more ( 0+ ), e.g., [0-9]* matches zero or more digits. It accepts all those in [0-9]+ plus the empty string.
Example: "a\+" matches "a+" and not a series of one or "a"s. ^ the caret is the anchor for the start of the string, or the negation symbol. Example: "^a" matches "a" at the start of the string. Example: "[^0-9]" matches any non digit. $ the dollar sign is the anchor for the end of the string.
Basically (0+1)* mathes any sequence of ones and zeroes. So, in your example (0+1)*1(0+1)* should match any sequence that has 1. It would not match 000 , but it would match 010 , 1 , 111 etc. (0+1) means 0 OR 1.
This should work
\+?\d+ Matches an optional + at the beginning of the line and digits after it
EDIT:
As of OP's request of clarification: 3423kk55 is matched because so it is the first part (3423). To match a whole string only use this instead:
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