$ g++ main.cpp
/tmp/ccxib5or.o: In function `main':
main.cpp:(.text+0x9e): undefined reference to `populate(warrior*, unsigned int)'
main.cpp:(.text+0xbc): undefined reference to `evolve(warrior*, unsigned int, unsigned int)'
main.cpp:(.text+0xd2): undefined reference to `dump(warrior*, unsigned int)'
collect2: ld returned 1 exit status