[QuantumTunnel]

Look it up on google preg functions in php :) Just use PHP's documentation you won't learn anything unless you go research it yourself :)

[houseinn2]

put your string in one variable.
make another variable valid char like "abc...xyz.ABC..XYZ012..9".
Check if the char in ur string is contained in valid char.
if yes,put it as it is
else,"-"