"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/016_for2.zig

@@ -0,0 +1,33 @@
+//
+// For loops also let you store the "index" of the iteration - a
+// number starting with 0 that counts up with each iteration:
+//
+//     for (items) |item, index| {
+//
+//         // Do something with item and index
+//
+//     }
+//
+// You can name "item" and "index" anything you want. "i" is a popular
+// shortening of "index". The item name is often the singular form of
+// the items you're looping through.
+//
+const std = @import("std");
+
+pub fn main() void {
+    // Let's store the bits of binary number 1101 in
+    // 'little-endian' order (least significant byte first):
+    const bits = [_]u8{ 1, 0, 1, 1 };
+    var value: u32 = 0;
+
+    // Now we'll convert the binary bits to a number value by adding
+    // the value of the place as a power of two for each bit.
+    //
+    // See if you can figure out the missing piece:
+    for (bits) |bit, ???| {
+        var place_value = std.math.pow(u32, 2, @intCast(u32, i));
+        value += place_value * bit;
+    }
+
+    std.debug.print("The value of bits '1101': {}.\n", .{value});
+}