Added Ex. 18 functions

18_functions.zig

@@ -0,0 +1,19 @@
+//
+// Functions! FUNctions! FUN!
+//
+const std = @import("std");
+
+pub fn main() void {
+    // The new function deepThought() should return the number 42. See below.
+    const answer = deepThought();
+    
+    std.debug.print("Answer to the Ultimate Question: {}\n", .{answer});
+}
+
+//
+// We're just missing a couple things here. One thing we're NOT missing is the
+// keyword 'pub', which is not needed here. Can you guess why?
+//
+??? deepThought() ??? {
+    return 42; // Number courtesy Douglas Adams
+}