I copied and pasted the following tutorial code and was able to compile it without any warnings/errors.
However, when I run it, it seems to go into a different video mode, but otherwise does absolutely nothing until I finally get bored and press escape which makes it all go away.
This is on a MacOS 10.12.2

I would expect this to make the screen red... but it's black.
I also tried 1,0,0 just in case it was expecting a 0-1 scale for the color.
But no... same result.

Please help. I feel very sad being stumped so badly before I've even begun.
Thanks

#include <stdio.h>
#include <allegro5/allegro.h>

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

ALLEGRO_DISPLAY *display = NULL;

if (!al_init()) {
fprintf(stderr, "failed to initialize allegro!\n");
return -1;
}

display = al_create_display(640, 480);
if (!display) {
fprintf(stderr, "failed to create display!\n");
return -1;
}

al_clear_to_color(al_map_rgb(255,0,0));

al_flip_display();

al_rest(10.0);

al_destroy_display(display);

return 0;
}

Hmm I tried your suggestions and still no luck. Maybe I'm doing something fundamentally wrong at an even earlier stage. I'm building with gcc... and running the a.out from the command line. Is there anything inherently wrong with that?

Here is the compile command I'm using:

gcc allegromain.c -I /usr/local/include -lallegro -lallegro_main -L /usr/local/lib -lallegro_image -lallegro_primitives

some of those libs probably aren't needed... they were from other tutorials I was attempting before I realized that they were all silently failing to work as intended.

I remember having difficulty with the Mac version of Code::Blocks, but there is a tutorial somewhere for setting it up with Xcode (as convoluted as the process was it works)

So here's the code again with the modifications based on the first suggestions.
This code, when run, makes my whole screen go dark. After about 5 seconds the screen comes back a dark color with an extra large mouse pointer. It stays that way indefinitely. When I press escape, it exits and there is a message in the terminal:
2017-02-15 21:24:47.564 a.out[39301:4520130] void * _Nullable NSMapGet(NSMapTable * _Nonnull, const void * _Nullable): map table argument is NULL

#include <stdio.h>
#include <allegro5/allegro.h>

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

ALLEGRO_DISPLAY *display = NULL;

if (!al_init()) {
fprintf(stderr, "failed to initialize allegro!\n");
return -1;
}
al_set_new_display_flags(ALLEGRO_WINDOWED);
display = al_create_display(320, 200);
if (!display) {
fprintf(stderr, "failed to create display!\n");
return -1;
}
al_set_target_backbuffer(display);
al_clear_to_color(al_map_rgb(255,0,0));

al_flip_display();

al_rest(10.0);

al_destroy_display(display);

return 0;
}

That list of steps allowed me to solve the issue...
But the exact step that solved the problem turned out to be horrifyingly simple:
Apparently there is another a.out somewhere on my system that was getting preferentially executed instead of the one in the current directory.

I can't believe it was that lame of a problem.
But what a relief to finally be able to proceed with learning to use allegro.
Thanks so much