The name of an item can be restricted to within a single file (but note this is not the default) by putting the word static in front of the ordinary definition:
e.g. static double sum;
Such an item is said to have ``internal linkage'', meaning internal to the file containing the program code. The scope of such a name is from the textual point of definition to the end of the file. i.e you can refer to it in any line follwoing the one in which it is defined.
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