Regex to split string into array of numbers and characters using PHP

Question

I have an arithmetic string that will be similar to the following pattern.

a. 1+2+3
b. 2/1*100
c. 1+2+3/3*100
d. (1*2)/(3*4)*100

Points to note are that
1. the string will never contain spaces.
2. the string will always be a combination of Numbers, Arithmetic symbols (+, -, *, /) and the characters '(' and ')'

I am looking for a regex in PHP to split the characters based on their type and form an array of individual string characters like below.
(Note: I cannot use str_split because I want numbers greater than 10 to not to be split.)

a. 1+2+3
output => [
0 => '1'
1 => '+'
2 => '2'
3 => '+'
4 => '3'
]

b. 2/1*100
output => [
0 => '2'
1 => '/'
2 => '1'
3 => '*'
4 => '100'
]`

c. 1+2+3/3*100

output => [
0 => '1'
1 => '+'
2 => '2'
3 => '+'
4 => '3'
5 => '/'
6 => '3'
7 => '*'
8 => '100'
]`

d. (1*2)/(3*4)*100

output => [
0 => '('
1 => '1'
2 => '*'
3 => '2'
4 => ')'
5 => '/'
6 => '('
7 => '3'
8 => '*'
9 => '4'
10 => ')'
11 => '*'
12 => '100'
]

Thank you very much in advance.

Answer 1

Use this regex :
(?<=[()/*+-])(?=[0-9()])|(?<=[0-9()])(?=[()/*+-])

It will match every position between a digit or a parenthesis and a operator or a parenthesis.
(?<=[()/*+-])(?=[0-9()]) matches the position with a parenthesis or an operator at the left and a digit or parenthesis at the right
(?<=[0-9()])(?=[()/*+-]) is the same but with left and right reversed.

Demo here