Условия

// Оператор if

if (month == 12 || month == 1 || month == 2) {
    season = "Winter";
}
else if (month ==3 || month == 4 || month == 5) {
    season = "Spring";
}
else if (month == 6 || month == 7 || month == 8) {
    season = "Summer";
}
else if (month == 9 || month == 10 || month == 11) {
    season = "Autumn";
}
else {
    season = "Fucking month";
}

// Оператор switch

switch ( выражение ) {

case значение1:
    break;

case значение2:
    break;

default:

}