How do I program using cat?

Question

In this xkcd comic:

they mention that real programmers use cat. Well, I was asking myself: how could you program using the cat command?

Answer 1

$ cat > hello.c
#include <stdio.h>

main(void) {
    printf("Hello, world.\n");
}
^D
$ gcc hello.c
$ ./a.out
Hello, world.