When an adjective precedes the noun, we use "de" instead "des" -- meaning "some." If you meant "of the," then you would still use "des"

As in English, French requires an article before the object.  In English you say 'I had a pleasant surprise'; you cannot say  'I had pleasant surprise'.  In English, however, you could say  'I had pleasant surprises', although it would be better to say  'I had some pleasant surprises'.  In French, you have to use the equivalent 'de', or in some cases, 'des' or 'les', depending on context.

N.B. I am not a native French speaker, so I stand to be corrected if in error about this.

merci! c'est tres utile! je comprends maintenant! 

I know i would need to put an article in this sentence. as its plurel here, I thought 'des" does make sense, but I am not really sure why 'de'. but thanks for your help Adrian!