C# 在 for 循环中嵌套 if/else

Question

我在 for 循环中有一个嵌套的 if/else 语句来确定一个值是否对数组值有效。它返回所有值都很好，但是如果 IF 是正确的，它仍然会执行 else 额外的 3 次。我以为一旦相等，它就会停止，但我想我在这里遗漏了一些东西。

string sectionChoice;
int ticketQuantity;
double ticketPrice, totalCost;
string[] section = { "orchestra", "mezzanine", "balcony", "general" };
double[] price = { 125.25, 62.00, 35.75, 55.50 };
bool isValidSection = false;

sectionChoice = GetSection();
ticketQuantity = GetQuantity();

for (int x = 0; x < section.Length; ++x)
{
    if (sectionChoice == section[x])
    {
        isValidSection = true;
        ticketPrice = price[x];

        totalCost = CalcTicketCost(ticketPrice, ticketQuantity);
        Console.Write("\n\nTotal cost for the tickets are: {0:c2}", totalCost);
    }
    else
        Console.Write("\n\nInvalid entry, {0} does not exist", sectionChoice);
}

当它有效时，它返回如下内容：

您的价格是 32.50。无效条目，x 不存在 无效条目，x 不存在 无效条目，x 不存在

Answer 1

您真正想做的是确定section 是否包含特定值，如果包含，则执行某些操作。直接检查那个：

if (section.Contains(sectionChoice))

您也不应该使用parallel arrays。而不是有两个数组，部分是价格，其中每个索引处的对象“组合”等于一个值，看起来你实际建模的是一种查找特定部分价格的方法。最好使用Dictionary 建模，它可以轻松查找特定键的值。在这里，您的关键是部分，价值是它的价格。

Dictionary<string, decimal> ticketsPrices = new Dictionary<string, decimal>()
{
    {"orchestra", 125.25m},
    //...
};
bool isValidSection = false;

string sectionChoice = GetSection();
int ticketQuantity = GetQuantity();

if (ticketsPrices.ContainsKey(sectionChoice))
{
    isValidSection = true;
    decimal ticketPrice = ticketsPrices[sectionChoice];

    decimal totalCost = CalcTicketCost(ticketPrice, ticketQuantity);
    Console.Write("\n\nTotal cost for the tickets are: {0:c2}", totalCost);
}
else
    Console.Write("\n\nInvalid entry, {0} does not exsist", sectionChoice);

Answer 2

您要查找的关键字是break;

break 将停止执行它所在的循环。如果你在嵌套循环中，它只会在最里面起作用。

与此相反的是continue。 Continue 停止该迭代并进入下一个迭代。

Here is an MSDN article explaining it more in depth

for (int x = 0; x < section.Length; ++x)
{
   if (sectionChoice == section[x])
   {
      isValidSection = true;
      ticketPrice = price[x];

      totalCost = CalcTicketCost(ticketPrice, ticketQuantity);
      Console.Write("\n\nTotal cost for the tickets are: {0:c2}", totalCost);
      break;
   }
   else
     Console.Write("\n\nInvalid entry, {0} does not exsist", sectionChoice);
 }

Answer 3

像这样获取所选项目的索引：

int i = section.IndexOf(sectionChoice);
if (i >= 0) {
    ticketPrice = price[i];
} else {
    // Not found!
}

但是，您的代码使用项目类会变得更加灵活

public class Section
{
    public string Name { get; set; }
    public decimal Price { get; set; }
}

通过这个类，您可以创建一个像这样的部分列表

List<Item> sections = new List<item> {
    new Section { Name = "orchestra", Price = 125.25 },
    new Section { Name = "mezzanine", Price = 62.00 },
    ...
};

现在你可以找到这样的部分：

Section section = sections.FirstOrDefault(s => s.Name == sectionChoice);
if (section != null ) ...

这样更容易向部分添加新属性。例如。您可以向其中添加一些剩余席位，而无需创建新数组。

Answer 4

您不想报告它对于每个不匹配的选项都是无效的选择：

for (int x = 0; x < section.Length; ++x)
{
    if (sectionChoice == section[x])
    {
        isValidSection = true;
        ticketPrice = price[x];

        totalCost = CalcTicketCost(ticketPrice, ticketQuantity);
        Console.Write("\n\nTotal cost for the tickets are: {0:c2}", totalCost);
        break;
     }
}

if (!isValidSection)
    Console.Write("\n\nInvalid entry, {0} does not exist", sectionChoice);

Answer 5

如果您希望在满足if 条件时停止迭代，您需要使用break 语句跳出循环：

for (int x = 0; x < section.Length; ++x)
{

    if (sectionChoice == section[x])
    {
        isValidSection = true;
        ticketPrice = price[x];

        totalCost = CalcTicketCost(ticketPrice, ticketQuantity);
        Console.Write("\n\nTotal cost for the tickets are: {0:c2}", totalCost);
        break;  // THIS IS THE IMPORTANT CHANGE
    }

}
if (!isValidSection) // TEST MOVED OUTSIDE OF LOOP
{
    Console.Write("\n\nInvalid entry, {0} does not exsist", sectionChoice);
}