When you define a structure, you tell C about the variables that describe the objects that belong to that structure.
*--------------------------------------------* | Description of variables: | <-- Description of the | for example, price and number | trade structure *--------------------------------------------* ^ ^ ^ | Instance of | Instance of | Instance of | | | *------------* *------------* *------------* | price 10.2 | | price 12.0 | | price 13.2 | <-- Descriptions of | number 600 | | number 100 | | number 200 | particular trade *------------* *------------* *------------* objects