simple regex to allow numbers from -20 to 20 with decimal points

how can I specify a regex that allows numbers from -20 to 20, including 0 and decimal points?

e.g all of the following are allowed:

20
19.99
5
0.5
0
1
3.45
-20
-17.20

>Solution :

If you’re looking for a regex for your task, you can use this one:

^-?1?\d(\.[\d]+)?$|^-?20$

Explanation:

• ^: start of number
• -?: optional minus
• 1?: optional 1 for tens
• \d: any digit for units
• (\.[\d]+)?: optional decimal places with any digit
• $: end of number

or

• ^: start of number
• -?: optional minus
• 20: 20
• $: end of number