Add a few example apps/demos in C, and make the kernel choose a random one to demonstrate every boot

apps/Makefile

@@ -1,4 +1,4 @@
-APPS := init
+APPS := init fib leap art memeater
 
 APPS_DIR := $(LUNA_ROOT)/apps
 APPS_SRC := $(APPS_DIR)/src

apps/src/art.c

@@ -0,0 +1,18 @@
+#include <stdio.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+int main()
+{
+    sleep(1);
+
+    syscall(SYS_paint, 0, 0, 400, 300, 0x000000FF);
+
+    sleep(1);
+
+    printf("Hello, colorful world!\n");
+
+    sleep(1);
+
+    printf("Press any key to restart.");
+}

apps/src/fib.c

@@ -0,0 +1,34 @@
+#include <luna.h>
+#include <stdio.h>
+#include <unistd.h>
+
+void fib_next(unsigned long int* a, unsigned long int* b)
+{
+    unsigned long int _a = *a;
+    unsigned long int _b = *b;
+    *a = *b;
+    *b = _a + _b;
+}
+
+int main()
+{
+    unsigned long int fib_a = 1;
+    unsigned long int fib_b = 1;
+
+    printf("Calculating the 50 first Fibonacci numbers...\n");
+
+    sleep(2);
+
+    printf("%lu\n", fib_a);
+
+    msleep(500);
+
+    for (int i = 0; i < 49; i++)
+    {
+        printf("%lu\n", fib_b);
+        fib_next(&fib_a, &fib_b);
+        msleep(500);
+    }
+
+    printf("\nDone, press any key to restart.\n");
+}

apps/src/leap.c

@@ -0,0 +1,38 @@
+#include <luna.h>
+#include <stdio.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+unsigned long random_year() // Return a year from 1000 to 2500.
+{
+    unsigned long result = syscall(SYS_rand);
+    return (result % 1500) + 1000;
+}
+
+int is_leap(unsigned long year)
+{
+    return ((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0);
+}
+
+int main()
+{
+    printf("Welcome to the Luna Leap Year Program!\n\n");
+
+    sleep(1);
+
+    printf("Choosing a random year between 1000 and 2500... ");
+
+    msleep(500);
+
+    unsigned long year = random_year();
+
+    printf("%lu!\n\n", year);
+
+    sleep(1);
+
+    printf("%lu is %s\n", year, is_leap(year) ? "a leap year!" : "not a leap year :(");
+
+    msleep(500);
+
+    printf("Press any key to restart.\n");
+}

apps/src/memeater.c

@@ -0,0 +1,17 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#define CHUNK 4194304 // 4 MB
+
+int main()
+{
+    printf("Welcome to memeater! This little program is designed to eat up all the memory on your system.\n");
+    sleep(1);
+    void* allocated = malloc(CHUNK);
+    do {
+        printf("Allocating 4 MB of memory... %lx\n", (unsigned long)allocated);
+        sleep(1);
+    } while ((allocated = malloc(CHUNK)));
+    printf("Out of memory.\n");
+}

kernel/src/main.cpp

@@ -124,7 +124,31 @@ extern "C" void _start()
         }
     });
 
-    Scheduler::load_user_task("bin/init");
+    int demo = Mersenne::get() % 5;
+
+    switch (demo)
+    {
+    case 0:
+        kinfoln("Loading demo: example init program");
+        Scheduler::load_user_task("bin/init");
+        break;
+    case 1:
+        kinfoln("Loading demo: first 50 fibonacci numbers");
+        Scheduler::load_user_task("bin/fib");
+        break;
+    case 2:
+        kinfoln("Loading demo: leap year calculator");
+        Scheduler::load_user_task("bin/leap");
+        break;
+    case 3:
+        kinfoln("Loading demo: painting program");
+        Scheduler::load_user_task("bin/art");
+        break;
+    case 4:
+        kinfoln("Loading demo: memory eating program");
+        Scheduler::load_user_task("bin/memeater");
+        break;
+    }
 
     kinfoln("Prepared scheduler tasks");