Variables in a loop

I'm trying to write a loop to read variables I receive from a form: <form ...> <input name=a1 value=..> <input name=a2 value=..> <input name=a3 value=..> <input name=a4 value=..> I'd like to get something like: for ($i=1; $i<=10; $i++) { $tab[$i]="a".$i ;} The expression "a".$i is actually a string, not a variable. Any idea how to "read" the value of that string? Thanks for your help. Jean-Louis