/tmp/ccgAiBzl.o: In function `stress_test(int, int, int)':
main.cpp:(.text+0x3de): undefined reference to `Num::operator*=(int)'
/tmp/ccgAiBzl.o: In function `main':
main.cpp:(.text+0xaca): undefined reference to `Num::operator+(Num const&)'
main.cpp:(.text+0xfbb): undefined reference to `Num::operator+(Num const&)'
main.cpp:(.text+0xfff): undefined reference to `Num::operator+(Num const&)'
main.cpp:(.text+0x110d): undefined reference to `Num::operator+(Num const&)'
main.cpp:(.text+0x114c): undefined reference to `Num::operator+(int)'
main.cpp:(.text+0x165e): undefined reference to `Num::operator*(Num const&)'
main.cpp:(.text+0x180e): undefined reference to `Num::operator*=(Num const&)'
main.cpp:(.text+0x1951): undefined reference to `Num::operator*=(int)'
main.cpp:(.text+0x19c6): undefined reference to `Num::operator*=(int)'
main.cpp:(.text+0x1b4f): undefined reference to `Num::operator*(Num const&)'
main.cpp:(.text+0x1b93): undefined reference to `Num::operator*(Num const&)'
main.cpp:(.text+0x1ca1): undefined reference to `Num::operator*(Num const&)'
main.cpp:(.text+0x1ce0): undefined reference to `Num::operator*(int)'
main.cpp:(.text+0x1d00): undefined reference to `Num::operator*=(Num const&)'
main.cpp:(.text+0x206a): undefined reference to `Num::operator*=(int)'
main.cpp:(.text+0x23c6): undefined reference to `Num::operator-(Num const&)'
main.cpp:(.text+0x2850): undefined reference to `Num::operator-(Num const&)'
main.cpp:(.text+0x2894): undefined reference to `Num::operator-(Num const&)'
main.cpp:(.text+0x29b0): undefined reference to `Num::operator-(Num const&)'
main.cpp:(.text+0x29ec): undefined reference to `Num::operator-(int)'
main.cpp:(.text+0x2a22): undefined reference to `Num::operator+(int)'
collect2: error: ld returned 1 exit status