What are the implications of declaring data types but never using them?

What are the possible problems if I declare a bunch of data types and never use them? Do they take up a lot of memory? Will they slow run time? If it is an array do I have to delete it at the end of the program? What if the array is defined inside a class and never used? Do I still have to delete it?

i.e.

Code:

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class declarearrays{
public:
double **darray;
double **darray2;
void function1();//function that initializes darray
void function2();//function that initializes darray2 with different parameters, may not be used.
};

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Do they take up a lot of memory?

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Well the whole library will be linked/loaded, so either you get a bigger executable or the whole library code is loaded into RAM later when it's used by the program.

Quote:

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Will they slow run time?

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No. You cannot expect the computer to spend time on something you don't use.

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Do I still have to delete it?

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No. It's very common to need only part of a library and link/load all of it.