can't really think of a শিরোনাম for this

when harry was sorted,it shows he has all his stuff(gryffindor robes,tie and scarf).but they don't know what house they are going to be in when at madam malkin's robes for all occasions,so how did he get them so soon.do আপনি think he got them at hogwarts,do students write letters to their parents and have them send it অথবা what


i wanna know what u guys think.because i'm completley lost.