Added ex 19,20 functions and pop quiz

20_quiz3.zig

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+//
+// Let's see if we can make use of some of things we've learned so far.
+// We'll create two functions: one that contains a "for" loop and one
+// that contains a "while" loop.
+//
+// Both of these are simply labeled "loop" below.
+//
+const std = @import( "std" );
+
+pub fn main() void {
+    const my_numbers = [4]u16{ 5,6,7,8 };
+
+    printPowersOfTwo(my_numbers);
+    std.debug.print("\n", .{});
+}
+
+//
+// You won't see this every day: a function that takes an array with
+// exactly four u16 numbers. This is not how you would normally pass
+// an array to a function. We'll learn about slices and pointers in
+// a little while. For now, we're using what we know.
+//
+// This function prints, but does not return anything.
+//
+fn printPowersOfTwo(numbers: [4]u16) ??? {
+    loop (numbers) |n| {
+        std.debug.print("{} ", .{twoToThe(n)});
+    }
+}
+
+//
+// This function bears a striking resemblance to twoToThe() in the last
+// exercise. But don't be fooled! This one does the math without the aid
+// of the standard library!
+//
+fn twoToThe(number: u16) ??? {
+    var n: u16 = 0;
+    var total: u16 = 1;
+
+    loop (n < number) : (n += 1) {
+        total *= 2;
+    }
+
+    return ???;
+}