I do have multiple files but I am not sure if they have been linked to the main file. I simply installed this project from the Internet and went ahead and opened the main.cpp file on Code::Blocks.
Here is the verbose build output:
g++.exe -std=c++11 -DSFML_STATIC -I"C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\SFML-2.5.1\include" -c "C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.cpp" -o "C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o"
g++.exe -L"C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\SFML-2.5.1\lib" -o "C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.exe" "C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o" "C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\SFML-2.5.1\lib\libsfml-graphics-s.a" "C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\SFML-2.5.1\lib\libsfml-window-s.a" "C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\SFML-2.5.1\lib\libsfml-system-s.a" "C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\SFML-2.5.1\lib\libopenal32.a" "C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\SFML-2.5.1\lib\libfreetype.a"
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x70e): undefined reference to `sf::String::String(char const*, std::locale const&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x72e): undefined reference to `sf::VideoMode::VideoMode(unsigned int, unsigned int, unsigned int)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x777): undefined reference to `sf::RenderWindow::RenderWindow(sf::VideoMode, sf::String const&, unsigned int, sf::ContextSettings const&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x7d4): undefined reference to `sf::View::View(sf::Rect<float> const&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x7ee): undefined reference to `sf::RenderTarget::setView(sf::View const&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x7fd): undefined reference to `GhostManager::GhostManager()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x80c): undefined reference to `Pacman::Pacman()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x844): undefined reference to `convert_sketch(std::array<std::string, 21ull> const&, std::array<Position, 4ull>&, Pacman&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x88f): undefined reference to `GhostManager::reset(unsigned char, std::array<Position, 4ull> const&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x972): undefined reference to `sf::Window::close()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x988): undefined reference to `sf::Window::pollEvent(sf::Event&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x9a9): undefined reference to `Pacman::get_dead()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x9eb): undefined reference to `Pacman::update(unsigned char, std::array<std::array<Cell, 21ull>, 21ull>&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xa15): undefined reference to `GhostManager::update(unsigned char, std::array<std::array<Cell, 21ull>, 21ull>&, Pacman&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xb24): undefined reference to `Pacman::set_animation_timer(unsigned short)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xb33): undefined reference to `sf::Keyboard::isKeyPressed(sf::Keyboard::Key)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xb51): undefined reference to `Pacman::get_dead()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xb95): undefined reference to `convert_sketch(std::array<std::string, 21ull> const&, std::array<Position, 4ull>&, Pacman&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xbe0): undefined reference to `GhostManager::reset(unsigned char, std::array<Position, 4ull> const&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xbef): undefined reference to `Pacman::reset()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xc27): undefined reference to `sf::Color::Color(unsigned char, unsigned char, unsigned char, unsigned char)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xc41): undefined reference to `sf::RenderTarget::clear(sf::Color const&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xc5e): undefined reference to `Pacman::get_dead()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xc8f): undefined reference to `draw_map(std::array<std::array<Cell, 21ull>, 21ull> const&, sf::RenderWindow&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xc9e): undefined reference to `Pacman::get_energizer_timer()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xcc1): undefined reference to `GhostManager::draw(bool, sf::RenderWindow&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xd25): undefined reference to `draw_text(bool, unsigned short, unsigned short, std::string const&, sf::RenderWindow&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xd63): undefined reference to `Pacman::draw(bool, sf::RenderWindow&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xd72): undefined reference to `Pacman::get_animation_over()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xddd): undefined reference to `draw_text(bool, unsigned short, unsigned short, std::string const&, sf::RenderWindow&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xe57): undefined reference to `draw_text(bool, unsigned short, unsigned short, std::string const&, sf::RenderWindow&)'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xe84): undefined reference to `sf::Window::display()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xea3): undefined reference to `sf::Window::isOpen() const'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0xeba): undefined reference to `sf::RenderWindow::~RenderWindow()'
C:\Users\...\Dropbox\PC\Documents\Project Task 2\Pacman-Main\Source\Main.o:Main.cpp:(.text+0x12ec): undefined reference to `sf::RenderWindow::~RenderWindow()'
collect2.exe: error: ld returned 1 exit status
Process terminated with status 1 (0 minute(s), 6 second(s))
36 error(s), 0 warning(s) (0 minute(s), 6 second(s))