C++ :: For Loop Theory For Tile Map Editing Program

Basically I have an tile class with the following variables: x, y, texture, and solid. I have created an array called tile MAP[map_tiles_x][map_tiles_y]. The object of the following snip-it of code is to loop through all of the tiles in the map placing their default values in each. For some reason this code does not work as planned, but in theory shouldn't it? I cannot see why it doesn't work. (BTW I do plan on open sourcing this map editor.

void init_map(){
for (int tile_y; tile_y < map_tiles_y; tile_y++){
for (int tile_x; tile_x < map_tiles_x; tile_x++){
MAP[tile_x][tile_y].x = tile_x * tile_size;
MAP[tile_x][tile_y].y = tile_y * tile_size;
MAP[tile_x][tile_y].solid = false;
std::cout << MAP[tile_x][tile_y].x << ", " << MAP[tile_x][tile_y].y;
} }

I should also add the effect of the code. Basically it only sets the default coordinates for the first object :/.