var caseCurrentPosition = 0;
var caseMinPosition = 0;
//var caseMaxPosition = 3;
function nextCase() {
    var newPosition = caseCurrentPosition + 1;
    if( newPosition > caseMaxPosition )
        newPosition = caseMinPosition;
    showCase( newPosition );
}

function prevCase() {
    var newPosition = caseCurrentPosition - 1;
    if( newPosition < caseMinPosition )
        newPosition = caseMaxPosition;
    showCase( newPosition );
}

function showCase( position ) {
    document.getElementById( "scrolling_" + caseCurrentPosition ).style.display = "none";
    document.getElementById( "scrolling_" + position ).style.display = "block";
    caseCurrentPosition = position;
}