JuniorTheoryCommon

If this file is the whole program, which build step reports an error?

C++

int twice(int x);

int main() {
    return twice(2);
}

Linking: twice has no definition anywhere

Expecting a compiler error: the declaration is enough to compile the call; only the linker looks for the body of twice.
Expecting 0 from a function with no body: there is nothing to run, so the program cannot be built at all.

What does the linker report when twice is defined in two different .cpp files?
How do the tools nm and c++filt help you find which object file lacks a symbol?

JuniorTheoryCommon

C++

int twice(int x);

int main() {
    return twice(2);
}

Linking: twice has no definition anywhere

Expecting a compiler error: the declaration is enough to compile the call; only the linker looks for the body of twice.
Expecting 0 from a function with no body: there is nothing to run, so the program cannot be built at all.

What does the linker report when twice is defined in two different .cpp files?
How do the tools nm and c++filt help you find which object file lacks a symbol?