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-rw-r--r--exercises/064_builtins.zig40
1 files changed, 28 insertions, 12 deletions
diff --git a/exercises/064_builtins.zig b/exercises/064_builtins.zig
index 508f8ed..018bf95 100644
--- a/exercises/064_builtins.zig
+++ b/exercises/064_builtins.zig
@@ -41,22 +41,38 @@ pub fn main() void {
var my_result: u4 = undefined;
var overflowed: bool = undefined;
overflowed = @addWithOverflow(u4, a, b, &my_result);
- //
+
+ // Check out our fancy formatting! b:0>4 means, "print
+ // as a binary number, zero-pad right-aligned four digits."
// The print() below will produce: "1101 + 0101 = 0010 (true)".
- // Let's make sense of this answer by counting up from 1101:
+ print("{b:0>4} + {b:0>4} = {b:0>4} ({})", .{ a, b, my_result, overflowed });
+
+ // Let's make sense of this answer. The value of 'b' in decimal is 5.
+ // Let's add 5 to 'a' but go one by one and see where it overflows:
//
- // Overflowed?
- // 1101 + 1 = 1110 No.
- // 1110 + 1 = 1111 No.
- // 1111 + 1 = 0000 Yes! (Real answer is 10000)
- // 0000 + 1 = 0001 No.
- // 0001 + 1 = 0010 No.
+ // a | b | result | overflowed?
+ // ----------------------------------
+ // 1101 + 0001 = 1110 | false
+ // 1110 + 0001 = 1111 | false
+ // 1111 + 0001 = 0000 | true (the real answer is 10000)
+ // 0000 + 0001 = 0001 | false
+ // 0001 + 0001 = 0010 | false
//
- // Also, check out our fancy formatting! b:0>4 means, "print
- // as a binary number, zero-pad right-aligned four digits."
- print("{b:0>4} + {b:0>4} = {b:0>4} ({})", .{ a, b, my_result, overflowed });
+ // In the last two lines the value of 'a' is corrupted because there was
+ // an overflow in line 3, but the operations of lines 4 and 5 themselves
+ // do not overflow.
+ // There is a difference between
+ // - a value, that overflowed at some point and is now corrupted
+ // - a single operation that overflows and maybe causes subsequent errors
+ // In practise we usually notice the overflowed value first and have to work
+ // our way backwards to the operation that caused the overflow.
+ //
+ // If there was no overflow at all while adding 5 to a, what value would
+ // 'my_result' hold? Write the answer in into 'expected_result'.
+ const expected_result: u8 = ???;
+ print(". Without overflow: {b:0>8}. ", .{expected_result});
- print(". Furthermore, ", .{});
+ print("Furthermore, ", .{});
// Here's a fun one:
//