maintain 0 at the start of a number

I have string of numbers that starts with a 0. I need to convert this to a number (str2num) but maintain the 0 at the start, as it represents a phone number.

example:

>> a = ('0123')

a =

0123

>> b = str2num(a)

b =

   123

Any suggestions on how to do this so that my answer would be 0123?

Answer 1

[Star Strider]

Try this:

a = ('0123');
b = sprintf('%04u', uint64(str2num(a)))

Answer 2

[Paul Murphy]

Its a tricky one because i need to first convert the string to a number and then to uint64 as this is the format that my course grader wants the output.