[英]Getting error “Use of unassigned local variable” in C#
我对编程很陌生,所以如果这是一个简单的解决方法,请原谅我。 关于我的字符串变量“ city”,我一直收到错误消息“使用未分配的局部变量”。 令我感到困惑的是,我还有一个名为“ centreName”的字符串变量,即使它也没有初始化,它也不会出现相同的错误。
该程序的目的是让用户输入科学中心及其所在城市的名称数据。我尝试将“ city”变量初始化为string city = null
和string city = ""
,但是当我运行该程序,输出将显示空白,而不是用户输入的内容。 我的“ centreName”变量不是这种情况。
我将包括我正在使用的两个类的编码。 请忽略我的方法,因为我尚未对其进行调整以适合此程序。 它们是我以前用于某些方法的较旧方法,因此此处不应用编码。
这是我收到错误的类:
class ScienceCentreApp
{
static void Main(string[] args)
{
string centreName;
string city;
decimal ticketPrice = 0;
int visitorCnt;
string[] dArray = new String[5];
int[] adultVisitors = new int[5];
decimal[] totalRevenue = new decimal[5];
char enterMoreData = 'Y';
ScienceCentreVisitation scv;
do
{
visitorCnt = GetData(out centreName, city, ticketPrice, dArray, adultVisitors, totalRevenue);
scv = new ScienceCentreVisitation(centreName, city, ticketPrice, dArray, adultVisitors, totalRevenue);
Console.Clear();
Console.WriteLine(scv);
Console.Write("\n\n\n\nDo you want to enter more data - " +
"(Enter y or n)? ");
if (char.TryParse(Console.ReadLine(), out enterMoreData) == false)
Console.WriteLine("Invalid data entered - " +
"No recorded for your respones");
} while (enterMoreData == 'y' || enterMoreData == 'y');
Console.ReadKey();
}
public static int GetData(out string centreName, string city, decimal ticketPrice, string[] dArray, int[] adultVisitors, decimal[] totalRevenue)
{
int i,
loopCnt;
Console.Clear();
Console.Write("Name of Centre: ");
centreName = Console.ReadLine();
Console.Write("City: ");
city = Console.ReadLine();
Console.Write("Ticket Price: ");
string inValue = Console.ReadLine();
ticketPrice = Convert.ToDecimal(inValue);
Console.Write("How many records for {0}? ", centreName);
string inValue1 = Console.ReadLine();
if (int.TryParse(inValue1, out loopCnt) == false)
Console.WriteLine("Invalid data entered - " +
"0 recorded for number of records");
for (i = 0; i < loopCnt; i++)
{
Console.Write("\nDate (mm/dd/yyyy): ");
dArray[i] = Console.ReadLine();
if (dArray[i] == "")
{
Console.WriteLine("No date entered - " +
"Unknown recorded for visits");
dArray[i] = "Unknown";
}
Console.Write("Number of One-Day Adult Visitors: ");
inValue1 = Console.ReadLine();
if (int.TryParse(inValue1, out adultVisitors[i]) == false)
Console.WriteLine("Invalid data entered - " +
"0 recorded for adults visited");
}
return i;
}
}
}
这是第一个正在调用的另一个类:
class ScienceCentreVisitation
{
private string centreName;
private string city;
private decimal ticketPrice;
private string[] visitDate;
private int[] adultVisitors;
private decimal[] totalRevenue;
//constructors
public ScienceCentreVisitation()
{
}
public ScienceCentreVisitation(string cent)
{
centreName = cent;
}
public ScienceCentreVisitation(string cent, string cit, decimal price, string[] date, int[] visit, decimal[] rev)
{
visitDate = new string[date.Length];
adultVisitors = new int[visit.Length];
totalRevenue = new decimal[rev.Length];
Array.Copy(date, 0, visitDate, 0, date.Length);
Array.Copy(visit, 0, adultVisitors, 0, adultVisitors.Length);
Array.Copy(rev, 0, totalRevenue, 0, rev.Length);
centreName = cent;
city = cit;
ticketPrice = price;
}
//properties
public string CentreName
{
get
{
return centreName;
}
set
{
centreName = value;
}
}
public string City
{
get
{
return city;
}
set
{
city = value;
}
}
public decimal TicketPrice
{
get
{
return ticketPrice;
}
set
{
ticketPrice = value;
}
}
public string[] VisitDate
{
get
{
return visitDate;
}
set
{
visitDate = value;
}
}
public int[] AdultVisitors
{
get
{
return adultVisitors;
}
set
{
adultVisitors = value;
}
}
public decimal[] TotalRevenue
{
get
{
return totalRevenue;
}
set
{
totalRevenue = value;
}
}
//methods
public decimal CalculateTotalRevenue()
{
decimal totalRev;
int cntOfValidEntries;
int total = 0;
foreach (int c in adultVisitors)
total += c;
cntOfValidEntries = TestForZeros();
totalRev = (decimal)total / cntOfValidEntries;
return totalRev;
}
public int TestForZeros()
{
int numberOfTrueVisits = 0;
foreach (int cnt in adultVisitors)
if (cnt != 0)
numberOfTrueVisits++;
return numberOfTrueVisits;
}
public int GetIndexOfLeastVisited()
{
int minVisIndex = 0;
for (int i = 1; i < adultVisitors.Length; i++)
if (adultVisitors[i] > adultVisitors[minVisIndex])
minVisIndex = i;
return minVisIndex;
}
public int GetLeastVisited()
{
return adultVisitors[GetIndexOfLeastVisited()];
}
public string GetDateWithLeastVisited()
{
return visitDate[GetIndexOfLeastVisited()];
}
public int GetIndexOfMostRevenue()
{
int maxRevIndex = 0;
for (int i = 1; i < totalRevenue.Length; i++)
if (totalRevenue[i] > totalRevenue[maxRevIndex])
maxRevIndex = i;
return maxRevIndex;
}
public decimal GetMostRevenue()
{
return totalRevenue[GetIndexOfMostRevenue()];
}
public string GetDateWithMostRevenue()
{
return visitDate[GetIndexOfMostRevenue()];
}
public override string ToString()
{
return "Name of Centre: " + centreName +
"\nCity: " + city +
"\nDate of Least One-Day Adult Visitors:\t\t" + GetDateWithLeastVisited() +
"\nNumber of Least One-Day Adult Visitors: \t\t" + GetLeastVisited() +
"\nDate of Most Total Revenue Collected:\t\t" + GetDateWithMostRevenue() +
"\nHighest Total Revenue Collected:\t\t" + GetMostRevenue();
}
}
}
提前致谢!
centreName
和city
之间的区别在于, centreName
用作out
参数。 这意味着您可以使用未初始化的变量来调用方法,因为可以确保在方法内部为变量分配一个值。
在您的情况下,在GetData
为centreName
和city
都分配了值,因此您可以安全地将string city
替换为out string city
。
centerName被声明为out参数(意味着当您离开方法的作用域时,它将保留您在方法内为其分配的最后一个值),因此将通过get数据对其进行初始化。 其余变量未通过get data调用设置,因为它们不是out参数。
在这一点上,C#通常认为out参数是不好的做法(我不会说其他语言)。 大多数情况下,它们掩盖了该方法的用途,在调用该方法(或错误地对其进行初始化)之后,很容易意外覆盖out参数之一的值。 不用使用out参数,而是创建一个包装数据的对象并返回它而不是int。
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