scanf() variable length specifier

Question

How can I use a variable to specify the max number of chars scanf() should read in?

For example using printf() you can use the * like so

Answer 1

You can't. You need to use something other than scanf(). A good and popular choice is fgets(), although its semantics are slightly different: fgets() will read a line of input, whereas scanf() with %s will read whitespace separated sequences of characters.

To use fgets(), you'd want something like:

fgets(string, MAXVAL, stdin);

If for some reason you really want to use scanf(), have a look at this question: How to prevent scanf causing a buffer overflow in C?