How add key to dictionary without value?

Question

in normally we should add key and value together in dictionary type. like:

myDict.Add(key1, value1);
myDict.Add(key2, value2);

I want to know, Is there any way to add key first, then insert its value? (not both of them at the same time)

Solution

If the value type of the dictionary is nullable, you could add a null value:

myDict.Add(key1, null);

If the value is non nullable, you can use a default value, either default or some out of range value, depending on your expected meaningful values.

myDict.Add(key1, default(int));
myDict.Add(key1, Int32.MinValue);

But

as mentioned in the comments, there is no discernible merit in doing this. You can add values at any time, there is no need to pre-initialize a dictionary with keys.