I think nobody spoke about this point yet. If I missed it while reading the answers, I am sorry, I didn’t mean to be redundant. The way of writing a dialog with a character who stutters should be different, in my opinion. I have seen many unsuccessful attempts in writing down the sound of the stutter. Inform yourself about blocks, repetition or prolongation stutters and try to recreate the sound while writing. If you need some inspiration, Stephen King did a good job in the novel It, because he didn’t use the cliched hyphens like “s-s-something” but actually wrote “suh-suh-something” (I don’t know if this example is accurate btw, it’s just to show an example). For blocks I would recommend to use “...” or just describe that the character is blocking. That’s it! Sorry if it was a bit long...