Convert String to numbers

Hey I've got a problem. I have to convert a String (200x1) that each line has four numbers:

0000

0001

0002

0003

...

...

...

to number, to be able to do operations. I used str2num but it comes error: Input must be a character vector or string scalar.

Answer 1

[Sean de Wolski]

s = ["0001" "0002"]

s = 1×2 string array
    "0001"    "0002"

n = double(s)

n = 1×2

1 2

[flashpode]

I do not want to change the 0000 0001 and those numbers I just want to operate with them