sub countt{
    ...
    my @arraystr =split(//,$string);#split the string acc. to each  al
+phabet and pass it to the array. 
    foreach my $alpha($string){
        if ($alpha =~ /t/i){ # if 't' is found
            $count++;        #increment the count
            return $count;   # 
        }
}
[download]

If you want to stick to your own approach, I see two issues with your original code:

• you create an array, but don't use it ... maybe you want to use arraystr in your loop
• inside the loop, you have the return; this ends your subroutine before all elements have been processed; you will want to move the return behind the loop...

HTH, Rata