num2str - leading zeros, is not working?

Hi,

i have the following problem.

I need to convert an integer into a string and i want a leading zero.

3.1 --> 03.1
21.2222 --> 21.2
1 --> 01.0

I tried :
i=3.1
disp(['i=',num2str(i,'%02.1d')])
but the result is i=3.1e+000

I tried
i=3.1
disp(['i=',num2str(i,'%02.1f)])
but the result is i=3.1 without the leading zero?

Any idea whats worng here?

THX