Moved exercises to exercises because exercises

exercises/18_functions.zig

@@ -0,0 +1,34 @@
+//
+// Functions! We've already seen a lot of one called "main()". Now let's try
+// writing one of our own:
+//
+//     fn foo(n: u8) u8 {
+//         return n+1;
+//     }
+//
+// The foo() function above takes a number "n" and returns a number that is
+// larger by one.
+//
+// If your function doesn't take any parameters and doesn't return anything,
+// it would be defined like main():
+//
+//     fn foo() void { }
+//
+const std = @import("std");
+
+pub fn main() void {
+    // The new function deepThought() should return the number 42. See below.
+    const answer: u8 = deepThought();
+    
+    std.debug.print("Answer to the Ultimate Question: {}\n", .{answer});
+}
+
+//
+// Please define the deepThought() function below.
+//
+// We're just missing a couple things. 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
+}