使用未分配的局部變量

Question

我必須建立一個程序來獲取比薩餅的直徑，並找到它可以容納多少個切片以及每個切片的面積（比薩餅），它用常數定義比薩餅的大小，但是“ int numberOfSlice”卻出錯了是說使用未分配的局部變量，甚至認為是在分配if語句。

class Program
{
    static void Main(string[] args)
    {
        //declarations of Constans

        const int SMALL_MIN = 12; 
        const int SMALL_MED = 16;
        const int MED_LARGE = 24;
        const int LARGE_XLARGE = 30;
        const int XL_MAX = 36;
        const int SMALL_SLICE = 8;
        const int MED_SLICE = 12;
        const int LARGE_SLICE = 16;
        const int XL_SLICES = 24;
        //declarations of varable
        double pizzaDiameter;
        int numberOfSlices = 0;
        double sliceArea;
        double radius; 
        string userInput = " ";


        Console.WriteLine("Please enter the diameter of your pizza:"); // tell user to input diameter 
        userInput = Console.ReadLine(); // gets userinput
        double.TryParse(userInput, out pizzaDiameter); // see if userinput is vaild


        if (pizzaDiameter >= SMALL_MIN && pizzaDiameter <= XL_MAX) // if in range will continue
        {

            // all the ranges for the pizzas 
            if (pizzaDiameter >= SMALL_MIN && pizzaDiameter < SMALL_MED)
            {
                numberOfSlices = (SMALL_SLICE);
            }

            else if (pizzaDiameter >= SMALL_MED && pizzaDiameter < MED_LARGE)
            {
                numberOfSlices = (MED_SLICE);
            }

            else if (pizzaDiameter >= MED_SLICE && pizzaDiameter < LARGE_XLARGE)
            {
                numberOfSlices = (LARGE_SLICE);
            }

            else if (pizzaDiameter >= LARGE_XLARGE && pizzaDiameter <= XL_MAX)

            {
                numberOfSlices = (XL_SLICES);
            }


            radius = pizzaDiameter / 2; // divides pizzaDiameter to get radius 


            sliceArea = Math.PI * Math.Pow(radius, 2) / numberOfSlices; // gets slice area

            sliceArea = Math.Round(sliceArea, 2); // rounds to 2 places

            // output of resluts 
            Console.WriteLine("\nA diameter of " + pizzaDiameter + " will yield " + numberOfSlices + " slices.");
            Console.WriteLine("\nEach slice will have an area of " + sliceArea + "\".");

            Console.WriteLine("\nPress any key to exit..."); // tells user to end program
            Console.ReadKey(); // readkey to end program


        }



        else // if the diameter was not in range will display this error 
        {
            Console.WriteLine("\nEntry Error ");
            Console.WriteLine("\nPizza must have a diameter in the range of 12\" to 36\" inclusive!");
            Console.WriteLine("please try again");

            Console.WriteLine("\nPress any key to end this application...");// tells user to end program
            Console.ReadKey(); // readkey to end program

        }      






    }
}

}

Answer 1

錯誤告訴您所有您需要了解的內容。 您的numberOfSlices變量未正確初始化。 使用它之前，必須在每個可能的代碼路徑中為其分配一個值。

嘗試在聲明時對其進行初始化：

int numberOfSlices = 0;

或者，您可以更仔細地構造if -block以避免此錯誤：

if (pizzaDiameter <= XL_MAX || pizzaDiameter >= SMALL_MIN)
{
    if (pizzaDiameter >= SMALL_MIN || pizzaDiameter < SMALL_MED)
    {
        numberOfSlices = (SMALL_SLICE);
    }
    ...
    else  // Note, you do not need the final `if` in this block
    {
        numberOfSlices = (XL_SLICES);
    }

    radius = pizzaDiameter/2;

    sliceArea = Math.PI * Math.Pow(radius, 2);

    Console.WriteLine("\nA diameter of " + pizzaDiameter + " will yield." + numberOfSlices + " slices.");
    Console.WriteLine("\nEach slice will have an area of " + sliceArea + "\".");
    Console.WriteLine("\nPress any key to exit...");
    Console.ReadKey();
}
else
{
    Console.WriteLine(" Entry Error ");
    Console.WriteLine("Pizza must have args diameter in the range of 12\" to 36\" inclusive!");
    Console.WriteLine("please try again");
    Console.WriteLine(" /nPress any key to end this application...");
    Console.ReadKey();
}

在此代碼中， numberOfSlices僅在if塊內部if ，該塊保證在使用之前為其分配值。

Answer 2

該變量仍未在外部else塊中分配：

if (pizzaDiameter <= XL_MAX || pizzaDiameter >= SMALL_MIN)
{
}
else
{
    // unassigned here
}

Answer 3

如果if (pizzaDiameter <= XL_MAX || pizzaDiameter >= SMALL_MIN)返回false，那么numberOfSlices不會被分配，並且以下行將失敗。

  Console.WriteLine("\nA diameter of " + pizzaDiameter + " will yield." + numberOfSlices + " slices.");

Answer 4

之所以得到該錯誤，是因為您僅在if塊中分配了它。
如果不滿足條件怎么辦？ 在那種情況下，它不會被初始化，因此會拋出該錯誤。

編譯器會在使用任何變量之前檢查每個可能的代碼路徑中的分配。

您需要做的是

int numberOfSlices=0; // Or whatever initial value you want to give
if (pizzaDiameter <= XL_MAX || pizzaDiameter >= SMALL_MIN)
{
}
else
{

}
//Then, even if you try to access it here, it won't throw any error.

注意：它不是由int的默認值 （即0）初始化的，因為它不是類的數據成員。