Use of unassigned local variable

Question

i have to build a program that takes the diameter of a pizza and finds how many slices it can hold and the area of each slice, the pizza, it defines the pizza size with constants, but a getting an error with "int numberOfSlice" it is saying use of unassigned local variable, even thought am assigning thought the if statements.

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

There error tells you everything you need to know. Your numberOfSlices variable isn't properly initialized. It must be assigned a value along every possible code path before you use it.

Try initializing it at the time it's declared:

int numberOfSlices = 0;

Or alternatively, you could construct your if -blocks more carefully to avoid this error:

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();
}

In this code, numberOfSlices is only used inside if block where it is guaranteed to be assigned a value before it is used.

Answer 2

The variable is still unassigned in the outer else block:

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不会被分配，并且以下行将失败。

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

Answer 4

You're getting the error because you've assigned it in only the if block.
What if the condition is not satisfied? In that case, it won't get initialized and hence throwing that error.

The compiler checks for the assignment in every possible code path before the usage of any variable.

What you need to do is,

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.

Note : It isn't initialized by the default value of int (ie 0) because it is not a data member of a class.