Create a regular expression that will check if the entire input consists of valid numbers between 200 to 255 inclusively.

Question

Hint: use ^ and $ anchors

Answer 1

The question is a bit ambiguous, so I'm going to assume the question is asking to create a regular expression that recognizes any number between 200 and 255 (inclusively) as the *only* text. For example, "232" is accepted by "hello232" is not.

We know that ^ is the regex character for "beginning of line" and $ is the "end of line" character, so our regular expression needs to be of the form ^EXP$

Since our goal is to recognize all the numbers between 200 and 255, we know that the first digit should always be 2. The second digit can range from 0 to 5 (inclusively). The third digit is a bit tricky, since 9 is valid in 249 but not in 259.

We can split the problem up into recognizing 200-249 and 250-255 pretty simply. Assuming | is used for "or" (some people use + among others) and that parenthesis and brackets are used just for grouping, we get:

^(2[0-4][0-9])|(25[0-5])$

Keep in mind different people and different programs use varying notation, this is just the notation I'm familiar with. This regex will only match strings that consist entirely of the numbers 200 through 255.