Is there a function to do this?

f(number,chars);

f(12,4) = '0012';

Answer 1

[Stephen23]

There is no need to manipulate the format string, it is much simpler to use the '*' option:

>> sprintf('%0*d',4,12)
ans = 0012

Answer 2

[Fangjun Jiang]

With this, will you be able to work out the function?

>> sprintf('%04d',12)

ans =

    '0012'

Answer 3

[Guillaume]

sprintf? Describing what you want in words would help

number = 12;
chars = 4;
formatstring = sprintf('%%0%dd', chars); %create format string %0{char}d' where {char} is the value of char
sprintf(formatstring, number)