使用未分配的局部变量

Question

我必须建立一个程序，它需要一个比萨的直径，并找出它可以容纳多少片以及每片的面积，比萨，它用常量定义比萨尺寸，但是获得与“int numberOfSlice”的错误是它使用未分配的局部变量，甚至认为分配思想if语句。

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

有错误告诉你需要知道的一切。您的numberOfSlices变量未正确初始化。在使用它之前，必须为每个可能的代码路径分配一个值。

尝试在它的声明的时候初始化它：

int numberOfSlices = 0; 

或者，你可以更仔细地构建您的if -blocks来避免这个错误：

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(); 
} 

在这段代码，numberOfSlices是仅在if块内使用，保证在使用之前为其分配一个值。

Answer 2

变量仍然是在外部else块未分配：

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不会得到分配及以下线路将失败。

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

Answer 4

由于您仅在if块中分配了错误，因此您会收到错误消息。
如果条件不满足会怎么样？在这种情况下，它不会被初始化，因此抛出该错误。

编译器会在使用任何变量之前检查每个可能的代码路径中的赋值。

你需要做的是，

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default value初始化（即0），因为它是不是一类的数据成员。