ADO.NET :: Create An Select SQL String By Some Search Fields

I want to create an Select SQL string by some search fields. Since I can't check the blank ones, otherwize it would look for blank, I have to do this on steps, adding them if they where not in blank, so, for that I am using something like this:

String SearchString = "SELECT * FROM Sala ";
String SelectWhere = "WHERE "; //This where is because I may receive all empty, so, the WHERE would make problems in the string.
If (TextClassroom.Text != "") {
SelectWhere += "(Classroom = " + Classroom.Text + ")";
}

But here is the issue. I may search for more than one at once, and that, would make me have to put an "AND" clause between them. How do I check that in the less number of lines as possible? I made a count variable, so I can count when it has been entered. But, getting to the third time it gets in, I have to check if the number is 1, or the number is 2, to see if I need to put an AND, right? And that would start making hard when we have, like, 10 fields. Is there an easier way to check when to put the AND without that many checks inside checks of empty texts?