public static void Main()
Console.WriteLine("請輸入分數");
int score = int.Parse(Console.ReadLine());
{ Console.WriteLine("優等");
else if(score >= 80 && score < 90)
{ Console.WriteLine("甲等");
else if(score >= 70 && score < 80)
{ Console.WriteLine("乙等");
else if(score >= 60 && score < 70)
{ Console.WriteLine("丙等");
{ Console.WriteLine("丁等");