What is a question mark in regular expression?

Answer 1

A question mark represents any single letter (or symbol).

In regular expression a question mark stands for a single symbol. So for example:

To write an expression representing all 4 letter words starting with #a# you have to use the expression #a???#. In this expression question marks represent second, third and fourth letter.

To express all words with at least one letter you can use expression ?*. In this expression the question mark represents a letter which must be present, the asterisk represents a string which may also be empty.

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Answer 2

Lydia Aguilar

In regular expressions, a question mark "?" is a quantifier that specifies that the preceding element in the pattern is optional. It matches the preceding element zero or one time.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.