尝试在控制台应用程序中完成库存系统，因此我被困在这一部分，以确保用户不能拥有重复的8位长ID号，我的问题如下。
基本上我不确定为什么这段代码不起作用，我可能在这里错过了一段非常明显的代码，感谢帮助，尝试改变已经存在的值，因此很可能忽略了一个值。< / p>
static int checkIDNumber(int ID)
{
// Check the number passed in & then loop through all the lines...
// If number is taken then output error, because id exists already
// Else allow the value to be used in the stock system.
int IDNumber = ID;
using (StreamReader sr = new StreamReader("Stockfile.txt"))
{
string lineValues;
while (sr.EndOfStream == false)
{
lineValues = sr.ReadLine();
if (lineValues.Contains(IDNumber.ToString()))
{
Console.WriteLine("Id number is currently already taken.");
}
else
{
return IDNumber;
}
}
}
}
我在另一个过程中从这一行传入我的值，并在本地范围内定义。
stockID = checkIDNumber(stockID);
以下是完整代码：
class Program
{
static void Main(string[] args)
{
char menuOption = '0';
while (menuOption != '3')
{
DisplayMenuOption();
menuOption = GetMenuOption();
switch (menuOption)
{
case '1':
AddStock();
break;
case '2':
CheckStock();
break;
case '3':
Console.WriteLine("Goodbye");
break;
default:
Console.WriteLine("That is not a valid option");
break;
}
}
// Keep it all happy for a screenshot ;)
Console.ReadLine();
}
static void DisplayMenuOption()
{
Console.WriteLine("Do you wish to Add Stock(1) or Check Stock(2) or Exit(3)?");
}
static void DisplayStockOption()
{
Console.WriteLine("Do you want to search by ID(1) or by Name(2), Delete current stock(3) or Exit(4)?");
}
static char GetMenuOption()
{
char userChoice = '0';
userChoice = Convert.ToChar(Console.ReadLine());
return userChoice;
}
static void CheckStock()
{
char menuOption = 'a';
while (menuOption != '4')
{
DisplayStockOption();
menuOption = GetMenuOption();
switch (menuOption)
{
case '1':
SearchID();
break;
case '2':
SearchName();
break;
case '3':
RemoveStock();
break;
case '4':
Console.WriteLine("Goodbye");
break;
default:
Console.WriteLine("That is not a valid option");
break;
}
}
}
static void RemoveStock()
{
List<string> tempList = new List<string>();
string lineValues = "";
bool found = false;
int ID = 0;
using (StreamReader sr = new StreamReader("Stockfile.txt"))
{
Console.Write("Please enter the ID number to delete: ");
ID = Convert.ToInt32(Console.ReadLine());
while (sr.EndOfStream == false)
{
lineValues = sr.ReadLine();
if (lineValues.Contains(ID.ToString()) == false)
{
tempList.Add(lineValues);
}
else
{
found = true;
}
}
}
if (found == true)
{
using (StreamWriter sw = new StreamWriter("Stockfile.txt", false))
{
for (int i=0; i < tempList.Count; i++)
{
sw.Write(tempList[i]);
sw.WriteLine();
}
}
}
}
static void SearchName()
{
using (StreamReader sr = new StreamReader("Stockfile.txt"))
{
string name;
Console.Write("Please enter the name: ");
name = Console.ReadLine();
while (sr.EndOfStream == false)
{
string lineValues = sr.ReadLine();
if (lineValues.Contains(name))
{
Console.WriteLine("{0}", lineValues);
}
else
{
Console.WriteLine("{0} does not exist in this stock system!",name); // Could try to match a similar string incase of spelling errors here, although after looking at it it may be a bit far for what is being required now, but in the real world application this would be a must else people would mistype words thus not having an exact match.
}
}
}
}
static void SearchID()
{
using (StreamReader sr = new StreamReader("Stockfile.txt"))
{
int IDNumber;
string lineValues;
Console.Write("Please enter the ID number: ");
IDNumber = Convert.ToInt32(Console.ReadLine());
while (sr.EndOfStream == false)
{
lineValues = sr.ReadLine();
if (lineValues.Contains(IDNumber.ToString()))
{
Console.WriteLine("{0}", lineValues);
}
else
{
Console.WriteLine("{0} does not exist in this stock system!", IDNumber); // Could try to match a similar string incase of spelling errors here, although after looking at it it may be a bit far for what is being required now, but in the real world application this would be a must else people would mistype words thus not having an exact match.
}
}
}
}
static int checkIDNumber(int ID)
{
// Check the number passed in & then loop through all the lines...
// If number is taken then output error, becuase id exists already
// Else allow the value to be used in the stock system.
using (StreamReader sr = new StreamReader("Stockfile.txt"))
{
int IDNumber;
string lineValues;
Console.Write("Please enter the ID number: ");
IDNumber = Convert.ToInt32(Console.ReadLine());
while (sr.EndOfStream == false)
{
lineValues = sr.ReadLine();
if (lineValues.Contains(IDNumber.ToString()))
{
Console.WriteLine("Id number is currently already taken.");
}
else
{
ID = IDNumber;
return ID;
}
}
}
}
static void AddStock(int IDNumber)
{
using (StreamWriter sw = new StreamWriter("Stockfile.txt", true))
{
int stockID = 0;
int stockQuantity = 0;
double stockPrice = 0.00;
string stockName = "";
string s = ""; // Being Lazy here, to convert to when needed.
while (stockID.ToString().Length != 8)
{
Console.Write("Please enter the stock ID number: ");
stockID = Convert.ToInt32(Console.ReadLine());
}
s = stockID.ToString();
sw.Write(s + "\t"); // Will only accept an 8 figure digit so is safe to have a single value here.
while (stockName.Length <= 2) // No fancy brands here......
{
Console.Write("Please enter the name of the stock: ");
stockName = Console.ReadLine();
}
s = stockName;
sw.Write(s + "\t");
while (stockQuantity < 1) // Running a small shop here...
{
Console.Write("Please enter the quanity of stock: ");
stockQuantity = Convert.ToInt32(Console.ReadLine());
}
s = stockQuantity.ToString();
sw.Write(s + "\t");
while (stockPrice < 0.01) // Running a very small shop....
{
Console.Write("Please enter the price of the stock: ");
stockPrice = Convert.ToDouble(Console.ReadLine());
}
s = stockPrice.ToString();
sw.Write(s + "\t");
sw.WriteLine(); // TO create the new line.....
}
}
}
}
答案 0 :(得分：7)
问题是你只是从else块中返回一个值。
无论程序通过代码执行哪条路径，您的方法都需要返回一个值。您可以通过多种方式解决此问题，具体取决于您的要求。例如，你可以在方法的底部有一个“catch-all”返回值，这样如果它通过你所有的测试（即if块）并到达底部，只要这是一个有意义的结果，它将返回catch-all值。
或者，您可以确保在每个代码路径中放置return语句。为此，您需要在return区块的if部分添加if，但您可能仍需要在while之外返回因为那可能永远不会执行。
同样，这完全取决于您的需求。
答案 1 :(得分：3)
至少在逻辑上，该文件只包含ID。例如，如果我输入“10”作为ID而文件是：
10
10
10
10
...
情况可能就是你知道实际永远不会发生，但编译器不能证明它不会。从编译器的“视角”来看，“可能发生”和“无法证明它不会发生”之间并没有真正的区别。
另外，你的逻辑错了。如果您知道用户请求了重复的ID，则无需检查文件的其余部分 - 您已经知道它是重复的。
现在，如果文件的第一行不是他们请求的ID，它将允许用户接受它。例如，如果用户请求“9”作为ID，则文件如下：
3 -- It only actually checks this line
5
9 -- Obviously the ID is already taken here but it'll never check this line
2
1
请参阅下面的评论：
// I'd suggest making this "bool" - they already know what the ID number is,
// so there's no point in returning it back to them
static int checkIDNumber(int ID)
{
// Check the number passed in & then loop through all the lines...
// If number is taken then output error, because id exists already
// Else allow the value to be used in the stock system.
int IDNumber = ID;
using (StreamReader sr = new StreamReader("Stockfile.txt"))
{
string lineValues;
// In general, you shouldn't explicitly compare to "true" or "false."
// Just write this as "!sr.EndOfStream"
while (sr.EndOfStream == false)
{
lineValues = sr.ReadLine();
if (lineValues.Contains(IDNumber.ToString()))
{
// In this case, you don't have to bother checking the rest of the file
// since you already know that the ID is taken
Console.WriteLine("Id number is currently already taken.");
}
else
{
// You actually can't return that at this point - you need to check
// the *entire* file before you conclude that it's not a duplicate
return IDNumber;
}
}
}
}