"999 is enough for anybody" triple-zero padding (#18)

When I hit 999 exercises, I will finally have reached the ultimate
state of soteriological release and no more exercises will be needed.
The cycle will be complete. All that will be left is perfect quietude,
freedom, and highest happiness.

exercises/042_pointers4.zig

@@ -0,0 +1,32 @@
+//
+// Now let's use pointers to do something we haven't been
+// able to do before: pass a value by reference to a function!
+//
+const std = @import("std");
+
+pub fn main() void {
+    var num: u8 = 1;
+    var more_nums = [_]u8{ 1, 1, 1, 1 };
+
+    // Let's pass a reference to num to our function and print it:
+    makeFive(&num);
+    std.debug.print("num: {}, ", .{num});
+
+    // Now something interesting. Let's pass a reference to a
+    // specific array value:
+    makeFive(&more_nums[2]);
+
+    // And print the array:
+    std.debug.print("more_nums: ", .{});
+    for (more_nums) |n| {
+        std.debug.print("{} ", .{n});
+    }
+
+    std.debug.print("\n", .{});
+}
+
+// This function should take a reference to a u8 value and set it
+// to 5.
+fn makeFive(x: *u8) void {
+    ??? = 5; // fix me!
+}