I am trying to run this main.cpp file:

#include "../include/world.h"
#include "../include/robot.h"

int main(int argc, char** argv) {

  char map[7][7] = {
    {'1', '1', '1', '1', '1', '1', '1'},
    {'1', '0', '0', '0', '0', '0', '1'},
    {'1', '0', '0', '0', '0', '0', '1'},
    {'1', '0', '0', '1', '1', '0', '1'},
    {'1', '0', '0', '1', '1', '0', '1'},
    {'1', '0', '0', '0', '0', '0', '1'},
    {'1', '1', '1', '1', '1', '1', '1'},
  };
  World w(map);

  w.addRobot(1, 1);

  w.run();
}

This is world.cpp:

#include <iostream>
#include <thread>
#include <chrono>
#include "world.h"

World::World(char map[7][7]) {
  for (int i = 0; i < 7; i++) {
    for (int j = 0; j < 7; j++) {
      map_[i][j] = map[i][j];
      std::cout << map_[i][j] << std::endl;
    }
  }
}

bool World::addRobot(int row, int col) {
  map_[row][col] = 'A';
  return true;
}

void World::run() {
  while (true) {
    display();
    std::this_thread::sleep_for(std::chrono::milliseconds(100));
  }
}

void World::display() {
  // "Clear" screen
  for (int i = 0; i < 20; i++){std::cout << std::endl;}

  for (auto & i : map_) {
    for (char j : i) {std::cout << j;}
    std::cout << std::endl;
  }
}

But this is the error:

/usr/bin/ld: /tmp/ccBztQoR.o: in function `main':
main.cpp:(.text+0xb1): undefined reference to `World::World(char (*) [7])'
/usr/bin/ld: main.cpp:(.text+0xc7): undefined reference to `World::addRobot(int, int)'
/usr/bin/ld: main.cpp:(.text+0xd3): undefined reference to `World::run()'
collect2: error: ld returned 1 exit status

Everything is accurately defined from what I can see. Where am I going wrong? How am I not defining it?