How can I put the index number as a value in a foreach?

I have the following code:

foreach (var SubTopic in Model开发者_运维知识库.SubTopic.Description)
{
 <option value="xxx">SubTopic</option>
}

I would like to find a way to insert the index number into xxx as value. 01 for the first, 02 for the second option line etc.

Is there an easy way to do this?

Use a for loop like

for (int i = 0; i < Model.SubTopic.Description.Count; i++)
    <option value="i">Model.SubTopic.Description[i]</option>

In C# you cannot directly access the actual index from within a foreach loop.

declare a variable with initial value 0 outside the loop and increment it inside the loop.

I am going to assume that the collection has no facility for retrieving items by index (like List) otherwise you would have used a simple for loop.

The foreach construct has no builtin mechanisms for doing this, but it is easy enough to accomplish with a helper class.

foreach (var item in ForEachHelper.WithIndex(Model.SubTopic.Description))
{
  Console.WriteLine("<option value=\"" + item.Index.ToString("00") + "\">" + item.Value + "</option");
}

And here is what the helper class looks like.

public static class ForEachHelper
{
    public sealed class Item<T>
    {
        public int Index { get; set; }
        public T Value { get; set; }
        public bool IsLast { get; set; }
    }

    public static IEnumerable<Item<T>> WithIndex<T>(IEnumerable<T> enumerable)
    {
        Item<T> item = null;
        foreach (T value in enumerable)
        {
            Item<T> next = new Item<T>();
            next.Index = 0;
            next.Value = value;
            next.IsLast = false;
            if (item != null)
            {
                next.Index = item.Index + 1;
                yield return item;
            }
            item = next;
        }
        if (item != null)
        {
            item.IsLast = true;
            yield return item;
        }            
    }
}