public static void Main()
double comC,comG,mathC,mathG,engC,engG,GPA;
Console.Write("input Com credit :");
comC = Convert.ToDouble(Console.ReadLine());
Console.Write("input Com grade :");
comG = Convert.ToDouble(Console.ReadLine());
Console.Write("input Math credit :");
mathC = Convert.ToDouble(Console.ReadLine());
Console.Write("input Math grade :");
mathG = Convert.ToDouble(Console.ReadLine());
Console.Write("input Eng credit :");
engC = Convert.ToDouble(Console.ReadLine());
Console.Write("input Eng grade :");
engG = Convert.ToDouble(Console.ReadLine());
GPA = (comC*comG + mathC*mathG + engC*engG)/(comC + mathC + engC);
Console.WriteLine("GPA = {0:F3}",GPA);