Welcome to the wonderful world of structures! ;-)
A structure, or a struct, is a collection of individual vars combined into a group. The group has a variable name, and each element in the struct has a name. To access a particular element in a struct, you access it by structure and element name. Remember that the element names in all structs of the same type follow the same structure.
The format is
struct_name.element_name. The var name befor the dot is the structure variable name, and the var name following the dot is the particular element name.
So, to answer your question, 'bi' is the name of a struct variable. 'biWidth' is the name of one of several elements in that struct. Combine them together with a dot between them and you get a unique element in a unique struct.
You could have two structs, bi1 and bi2. bi1.biWidth and bi2.biWidth have no relation to each other, except that they will be of the same type, thanks to the struct definition.
For more, consult the class materials. ;-)
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