Question

What is the purpose of defining a function without statements?
I have a C++ file with a list of functions defined without statements and they are not used anywhere else in the script. Does this mean they are defined in some other file?

Answer 1

What is the purpose of defining a function without statements?

This phrase has no meaning. But I suspect you are referring to function declaration statements that do not also contain a definition (or implementation) of said function.

void foo();  // Declaration (may be used as long as definition is linked)

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Does this mean they are defined in some other file?

And, yes, typically the definitions may be found in other translation units, that are linked together to create the final executable.

void foo() { // Defining declaration (or just "definition")
   /* ... */
}

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The typical C++ build process should be explained fairly thoroughly in your C++ book.