Updating multiple rows in table in sql server

Question

Hi Friends,i have small problem abt inserting data into multiple rows.Like this 

from the frontend we pass values like 

   string p=12,15,16

In table we have rows like

      sno   sname   marks

       1       Ravi       62

       2       Kumar    23

       3       Kumar    10

       4       kumar     8

i want put p(12,15,16) values to this table where ravi is there.

   For first Ravi--12

         second Ravi--15

         third-------16

I want without using sno.

Can any one help me?