C＃中的大小写/转换语句

Question

I wanted to know if there's a way to declare a lot of case statements without having to write all of them. For example, my code:

            switch (Weight)
            {
                case 0 to 2;
                    ShippingCost = "3.69";

                case 3 to 4;
                    ShippingCost = "4.86";

                case 5 to 6;
                    ShippingCost = "5.63";

                case 7 to 8;
                    ShippingCost = "5.98";

                case 9 to 10;
                    ShippingCost = "6.28";

                case 11 to 30;
                    ShippingCost = "15.72";

            }

I started converting VB to C# and realized that in order to have more than one case statements you have to declare them. As you can see I have 11 to 30 and do not wanna have all those lines.

Answer 1

You cannot use comparisons in C# as you can in VB. You can however use fall-through cases, like so:

case 0:
case 1:
case 2:
  ShippingCost = "3.69";
  break;

case 3:
case 4:
  ShippingCost = "4.86";
  break;

Note that non-empty cases require either a throw , return or, break statement. Also note that you can only fall-through on empty cases.

Edit:

For completeness, as others have pointed out, it is probably more sensible in this case to use a series of if statements, like so:

if(Weight<=2) {
  ShippingCost = "3.69";
}
else if(Weight <= 4) {
  ShippingCost = "4.86";
}
... etc

Answer 2

There is direct equivalent in C#, however, you can use fall-through so you don't have to repeat the implementation:

switch (Weight)
{
    case 0:
    case 1:
    case 2:
       ShippingCost = "3.69";
       break;
       ...

If statements would probably suit you much better in this scenario:

if(Weight >= 0 && Weight <= 2){
    ShippingCost = "3.69";
} else if(Weight >= 3 && Weight <= 4){
    ShippingCost = "4.86";
}
...

Answer 3

Try like this: This solutions removes the need to write && in your else if statements

if(Weight >= 11 && Weight <= 30)
{
   ShippingCost = "15.72";
}
else if(Weight >= 9)
{
   ShippingCost = "6.28";
}
else if(Weight >= 7)
{
   ShippingCost = "5.98";
}
else if(Weight >= 5)
{
   ShippingCost = "5.63";
}
else if(Weight >= 3)
{
   ShippingCost = "4.86";
}
else if(Weight >= 0)
{
   ShippingCost = "3.69";
}

Answer 4

You could also write it as a Linq one liner:

var ShippingCost = (new[] { new { w = 2, p = "3,69" }, 
                            new { w = 4, p = "4.86" }, 
                            new { w = 6, p = "5.63" }, 
                            new { w = 8, p = "5.98" }, 
                            new { w = 10, p = "6.28" }, 
                            new { w = 30, p = "15.72" }})
             .First(x => Weight <= x.w).p;

You would, as others have already stated, want to make sure that shipping for items weighing more than 30 is also handled correctly.

Answer 5

How bout just using this sort of approach

private static double GetShippingCost(double weight)
{
    if (weight > 30) throw new ArgumentException("Weight over allowed maximum", "weight");

    if (weight <= 2) return 3.69;
    if (weight <= 4) return 4.86;
    if (weight <= 6) return 5.63;
    if (weight <= 8) return 5.98;
    if (weight <= 10) return 6.28;
    if (weight <= 30) return 15.72;

}

Answer 6

An alternative to using a case would be to write some kind of class to do the mapping, for example:

public sealed class CostsPerWeight
{
    class CostPerWeight
    {
        public int Low;
        public int High;
        public double Cost;
    }

    readonly List<CostPerWeight> costs = new List<CostPerWeight>();

    public CostsPerWeight Add(int low, int high, double result)
    {
        // Error handling omitted for brevity. 
        // Real code should check that low < high and that ranges do not overlap.

        costs.Add(new CostPerWeight { Low = low, High = high, Cost = result } );
        return this;
    }

    public double Cost(int weight)
    {
        // This throws if the weight isn't in the list.
        // If that's not what you want, you'd have to add extra error handling here.
        return costs.First(x => x.Low <= weight && weight <= x.High).Cost;
    }
}

Which you would use like this (I've used doubles instead of strings for the costs for this example, but you can use whatever type you need):

var costs = new CostsPerWeight()
    .Add( 0,  2,  3.69)
    .Add( 3,  4,  4.86)
    .Add( 5,  6,  5.63)
    .Add( 7,  8,  5.98)
    .Add( 9, 10,  6.28)
    .Add(11, 30, 15.72);

double shippingCost = costs.Cost(weight);

If you have a lot of these switch statements in VB, it would be worth considering this approach.

(The advantage of using this instead of a Linq one-liner is simply that it's easier to document and unit test. You could also create a CostsPerWeight class instance and pass it around - useful for decoupling code, dependency-injection and for unit testing.)

It does seem to me that the concept of looking up a cost based on a weight is crying out to be encapsulated in a class, rather than embedded piecemeal in various parts of the code.

Here's a more extended example of CostsPerWeight with more error handling:

public class CostsPerWeight
{
    class CostPerWeight
    {
        public int Low;
        public int High;
        public double Cost;
    }

    readonly List<CostPerWeight> costs = new List<CostPerWeight>();

    double min = double.MaxValue;
    double max = double.MinValue;
    double costForMin;

    public CostsPerWeight Add(int low, int high, double cost)
    {
        if (low > high)
            throw new ArgumentException(nameof(low) + " must be less than " + nameof(high));

        if (cost < 0)
            throw new ArgumentOutOfRangeException(nameof(cost), "cost must be greater than zero");

        costs.Add(new CostPerWeight { Low = low, High = high, Cost = cost } );

        if (low < min)
        {
            min = low;
            costForMin = cost;
        }

        if (high > max)
            max = high;

        return this;
    }

    public double Cost(int weight)
    {
        if (weight < min)
            return costForMin;

        if (weight > max)
            throw new InvalidOperationException($"Weight {weight} is out of range: Must be <= {max}");

        return costs.First(x => x.Low <= weight && weight <= x.High).Cost;
    }
}

Answer 7

The clearest way is to put your data into objects instead.

  private struct ShippingCost
  {
      public int MinWeight;
      public int MaxWeight;
      public decimal Cost;

      public ShippingCost(int min, int max, decimal cost)
      {
         MinWeight = min;
         MaxWeight = max;
         Cost = cost;
      }
  }

  private List<ShippingCost> Costs = new List<ShippingCost>
  {
      new ShippingCost(0, 2, 3.69m),
      new ShippingCost(3, 4, 4.86m),
      new ShippingCost(5, 6, 5.63m),
      new ShippingCost(7, 8, 5.98m),
      new ShippingCost(9, 10, 6.28m),
      new ShippingCost(11, 30, 15.72m),
  };

  // Choose shipping cost
  public decimal CalcShippingCost(int weight)
  {
      foreach (ShippingCost sc in Costs)
      {
          if (weight >= sc.MinWeight && weight <= sc.MaxWeight)
              return sc.Cost;
      }

      return 0.00m;     // default cost
  }

Answer 8

You can't do that in C#. The best option if your max value for weight is 30 is to the use the default case.

Otherwise, if you don't want something like

case 11:
case 12:
case 13:
....
case 28:
case 29:
case 30:

an "oldschool" if/else if will be the the most readable solution

Answer 9

I'd recommend storing the data in a container and iterating through the container. You could create your own class or use a .net class like Tuple:

var shippingCostsByWeight = new List<Tuple<int, int, string>>
{
    new Tuple<int, int, string>(0, 2, "3.69"),
    new Tuple<int, int, string>(3, 4, "4.86"),
    new Tuple<int, int, string>(5, 6, "5.63"),
    new Tuple<int, int, string>(7, 8, "5.98"),
    new Tuple<int, int, string>(9, 10, "6.28"),
    new Tuple<int, int, string>(11, 30, "15.72"),
};

ShippingCost = shippingCostsByWeight
                .First(tuple => weight >= tuple.Item1 && weight <= tuple.Item2).Item3;

Answer 10

You could use a fall-through case switch statement, which goes as the following:

case 0:
case 1:
case 2:
  shippingCost = "3.69";
  break;

... and so on

Which will cause 0 to set shippingCost to 3.69 aswell as 1 and 2. :)
That would be my Solution to this