Add test programs to github.

tests/hellothreads/hellothreads.cpp

@@ -0,0 +1,41 @@
+#include <string.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <unistd.h>
+
+// Global variable:
+int i = 2;
+
+void bar (int v) {
+    printf("bar: %i\n", v);
+    sleep(20);
+    printf("bar: %i\n", v);
+}
+
+void* foo (void* p) {
+    // Print value received as argument:
+    printf("foo: Value recevied as argument in starting routine: ");
+    printf("%i\n", *(int*)p);
+
+    bar(*(int*)p);
+
+    // Return reference to global variable:
+    pthread_exit(&i);
+}
+
+int main (void) {
+    // Declare variable for thread's ID:
+    pthread_t id;
+
+    int j = 1;
+    pthread_create(&id, NULL, foo, &j);
+
+    int* ptr;
+
+    // Wait for foo() and retrieve value in ptr;
+    pthread_join(id, (void**)&ptr);
+
+    printf("Value recevied by parent from child: ");
+    printf("%i\n", *ptr);
+}
+