Added ex 19,20 functions and pop quiz

19_functions2.zig

@@ -0,0 +1,28 @@
+//
+// Now let's use a function that takes a parameter.
+//
+const std = @import( "std" );
+
+pub fn main() void {
+    std.debug.print("Powers of two: {} {} {} {}\n", .{
+        twoToThe(1),
+        twoToThe(2),
+        twoToThe(3),
+        twoToThe(4),
+    });
+}
+
+//
+// Oops! We seem to have forgotten something here. Function
+// parameters look like this:
+//
+//   fn myFunction( number: u8, is_lucky: bool ) {
+//       ...
+//   }
+//
+// As you can see, we declare the type of the parameter, just
+// like we declare the types of variables, with a colon ":".
+//
+fn twoToThe(???) u32 {
+    return std.math.pow(u32, 2, my_number);
+}