Add solutions

exercises/001_hello.zig

@@ -16,6 +16,6 @@
 //
 const std = @import("std");
 
-fn main() void {
+pub fn main() void {
     std.debug.print("Hello world!\n", .{});
 }

exercises/002_std.zig

@@ -11,7 +11,7 @@
 // Please complete the import below:
 //
 
-??? = @import("std");
+const std = @import("std");
 
 pub fn main() void {
     std.debug.print("Standard Library.\n", .{});

exercises/003_assignment.zig

@@ -34,12 +34,12 @@
 const std = @import("std");
 
 pub fn main() void {
-    const n: u8 = 50;
+    var n: u8 = 50;
     n = n + 5;
 
-    const pi: u8 = 314159;
+    const pi: u32 = 314159;
 
-    const negative_eleven: u8 = -11;
+    const negative_eleven: i8 = -11;
 
     // There are no errors in the next line, just explanation:
     // Perhaps you noticed before that the print function takes two

exercises/004_arrays.zig

@@ -27,7 +27,7 @@ pub fn main() void {
     // (Problem 1)
     // This "const" is going to cause a problem later - can you see what it is?
     // How do we fix it?
-    const some_primes = [_]u8{ 1, 3, 5, 7, 11, 13, 17, 19 };
+    var some_primes = [_]u8{ 1, 3, 5, 7, 11, 13, 17, 19 };
 
     // Individual values can be set with '[]' notation.
     // Example: This line changes the first prime to 2 (which is correct):
@@ -40,11 +40,11 @@ pub fn main() void {
     // (Problem 2)
     // Looks like we need to complete this expression. Use the example
     // above to set "fourth" to the fourth element of the some_primes array:
-    const fourth = some_primes[???];
+    const fourth = some_primes[3];
 
     // (Problem 3)
     // Use the len property to get the length of the array:
-    const length = some_primes.???;
+    const length = some_primes.len;
 
     std.debug.print("First: {}, Fourth: {}, Length: {}\n", .{
         first, fourth, length,

exercises/005_arrays2.zig

@@ -25,12 +25,12 @@ pub fn main() void {
     // (Problem 1)
     // Please set this array concatenating the two arrays above.
     // It should result in: 1 3 3 7
-    const leet = ???;
+    const leet = le ++ et;
 
     // (Problem 2)
     // Please set this array using repetition.
     // It should result in: 1 0 0 1 1 0 0 1 1 0 0 1
-    const bit_pattern = [_]u8{ ??? } ** 3;
+    const bit_pattern = [_]u8{ 1, 0, 0, 1 } ** 3;
 
     // Okay, that's all of the problems. Let's see the results.
     //

exercises/006_strings.zig

@@ -24,18 +24,18 @@ pub fn main() void {
     // (Problem 1)
     // Use array square bracket syntax to get the letter 'd' from
     // the string "stardust" above.
-    const d: u8 = ziggy[???];
+    const d: u8 = ziggy[4];
 
     // (Problem 2)
     // Use the array repeat '**' operator to make "ha ha ha ".
-    const laugh = "ha " ???;
+    const laugh = "ha " ** 3;
 
     // (Problem 3)
     // Use the array concatenation '++' operator to make "Major Tom".
     // (You'll need to add a space as well!)
     const major = "Major";
     const tom = "Tom";
-    const major_tom = major ??? tom;
+    const major_tom = major ++ " " ++ tom;
 
     // That's all the problems. Let's see our results:
     std.debug.print("d={u} {s}{s}\n", .{ d, laugh, major_tom });

exercises/007_strings2.zig

@@ -15,9 +15,9 @@ const std = @import("std");
 
 pub fn main() void {
     const lyrics =
-        Ziggy played guitar
+        \\Ziggy played guitar
-        Jamming good with Andrew Kelley
+        \\Jamming good with Andrew Kelley
-        And the Spiders from Mars
+        \\And the Spiders from Mars
     ;
 
     std.debug.print("{s}\n", .{lyrics});

exercises/008_quiz.zig

@@ -19,7 +19,7 @@ pub fn main() void {
     // the idiomatic type to use for array indexing.
     //
     // There IS a problem on this line, but 'usize' isn't it.
-    const x: usize = 1;
+    var x: usize = 1;
 
     // Note: When you want to declare memory (an array in this
     // case) without putting anything in it, you can set it to
@@ -33,10 +33,11 @@ pub fn main() void {
     lang[0] = letters[x];
 
     x = 3;
-    lang[???] = letters[x];
+    lang[1] = letters[x];
 
-    x = ???;
+    // x = letters.len - 1;
-    lang[2] = letters[???];
+    x = letters.len - 1;
+    lang[2] = letters[x];
 
     // We want to "Program in Zig!" of course:
     std.debug.print("Program in {s}!\n", .{lang});

exercises/009_if.zig

@@ -21,7 +21,7 @@
 const std = @import("std");
 
 pub fn main() void {
-    const foo = 1;
+    const foo: bool = true;
 
     // Please fix this condition:
     if (foo) {

exercises/010_if2.zig

@@ -10,7 +10,7 @@ pub fn main() void {
 
     // Please use an if...else expression to set "price".
     // If discount is true, the price should be $17, otherwise $20:
-    const price: u8 = if ???;
+    const price: u8 = if (discount) 17 else 20;
 
     std.debug.print("With the discount, the price is ${}.\n", .{price});
 }

exercises/011_while.zig

@@ -21,7 +21,7 @@ pub fn main() void {
     var n: u32 = 2;
 
     // Please use a condition that is true UNTIL "n" reaches 1024:
-    while (???) {
+    while (n < 1024) {
         // Print the current number
         std.debug.print("{} ", .{n});
 

exercises/012_while2.zig

@@ -25,7 +25,7 @@ pub fn main() void {
 
     // Please set the continue expression so that we get the desired
     // results in the print statement below.
-    while (n < 1000) : ??? {
+    while (n < 1000) : (n *= 2) {
         // Print the current number
         std.debug.print("{} ", .{n});
     }

exercises/013_while3.zig

@@ -24,8 +24,8 @@ pub fn main() void {
     while (n <= 20) : (n += 1) {
         // The '%' symbol is the "modulo" operator and it
         // returns the remainder after division.
-        if (n % 3 == 0) ???;
+        if (n % 3 == 0) continue;
-        if (n % 5 == 0) ???;
+        if (n % 5 == 0) continue;
         std.debug.print("{} ", .{n});
     }
 

exercises/014_while4.zig

@@ -18,7 +18,7 @@ pub fn main() void {
     // Oh dear! This while loop will go forever?!
     // Please fix this so the print statement below gives the desired output.
     while (true) : (n += 1) {
-        if (???) ???;
+        if (n == 4) break;
     }
 
     // Result: we want n=4

exercises/015_for.zig

@@ -15,7 +15,7 @@ pub fn main() void {
 
     std.debug.print("A Dramatic Story: ", .{});
 
-    for (???) |???| {
+    for (story) |scene| {
         if (scene == 'h') std.debug.print(":-)  ", .{});
         if (scene == 's') std.debug.print(":-(  ", .{});
         if (scene == 'n') std.debug.print(":-|  ", .{});

exercises/016_for2.zig

@@ -25,7 +25,7 @@ pub fn main() void {
     // the value of the place as a power of two for each bit.
     //
     // See if you can figure out the missing pieces:
-    for (bits, ???) |bit, ???| {
+    for (bits, 0..) |bit, i| {
         // Note that we convert the usize i to a u32 with
         // @intCast(), a builtin function just like @import().
         // We'll learn about these properly in a later exercise.

exercises/017_quiz2.zig

@@ -9,18 +9,18 @@
 // Let's go from 1 to 16. This has been started for you, but there
 // are some problems. :-(
 //
-const std = import standard library;
+const std = @import("std");
 
-function main() void {
+pub fn main() void {
     var i: u8 = 1;
     const stop_at: u8 = 16;
 
     // What kind of loop is this? A 'for' or a 'while'?
-    ??? (i <= stop_at) : (i += 1) {
+    while (i <= stop_at) : (i += 1) {
         if (i % 3 == 0) std.debug.print("Fizz", .{});
         if (i % 5 == 0) std.debug.print("Buzz", .{});
         if (!(i % 3 == 0) and !(i % 5 == 0)) {
-            std.debug.print("{}", .{???});
+            std.debug.print("{}", .{i});
         }
         std.debug.print(", ", .{});
     }

exercises/018_functions.zig

@@ -25,6 +25,6 @@ pub fn main() void {
 // We're just missing a couple things. One thing we're NOT missing is the
 // keyword "pub", which is not needed here. Can you guess why?
 //
-??? deepThought() ??? {
+pub fn deepThought() u8 {
     return 42; // Number courtesy Douglas Adams
 }

exercises/019_functions2.zig

@@ -22,7 +22,7 @@ pub fn main() void {
 // You'll need to figure out the parameter name and type that we're
 // expecting. The output type has already been specified for you.
 //
-fn twoToThe(???) u32 {
+fn twoToThe(comptime my_number: u32) u32 {
     return std.math.pow(u32, 2, my_number);
     // std.math.pow(type, a, b) takes a numeric type and two
     // numbers of that type (or that can coerce to that type) and

exercises/020_quiz3.zig

@@ -21,8 +21,8 @@ pub fn main() void {
 //
 // This function prints, but does not return anything.
 //
-fn printPowersOfTwo(numbers: [4]u16) ??? {
+fn printPowersOfTwo(numbers: [4]u16) void {
-    loop (numbers) |n| {
+    for (numbers) |n| {
         std.debug.print("{} ", .{twoToThe(n)});
     }
 }
@@ -31,13 +31,13 @@ fn printPowersOfTwo(numbers: [4]u16) ??? {
 // exercise. But don't be fooled! This one does the math without the aid
 // of the standard library!
 //
-fn twoToThe(number: u16) ??? {
+fn twoToThe(number: u16) u16 {
     var n: u16 = 0;
     var total: u16 = 1;
 
-    loop (n < number) : (n += 1) {
+    while (n < number) : (n += 1) {
         total *= 2;
     }
 
-    return ???;
+    return total;
 }

exercises/021_errors.zig

@@ -9,7 +9,7 @@
 // "TooSmall". Please add it where needed!
 const MyNumberError = error{
     TooBig,
-    ???,
+    TooSmall,
     TooFour,
 };
 
@@ -26,7 +26,7 @@ pub fn main() void {
         if (number_error == MyNumberError.TooBig) {
             std.debug.print(">4. ", .{});
         }
-        if (???) {
+        if (number_error == MyNumberError.TooSmall) {
             std.debug.print("<4. ", .{});
         }
         if (number_error == MyNumberError.TooFour) {

exercises/022_errors2.zig

@@ -19,7 +19,7 @@ const std = @import("std");
 const MyNumberError = error{TooSmall};
 
 pub fn main() void {
-    var my_number: ??? = 5;
+    var my_number: MyNumberError!u8 = 5;
 
     // Looks like my_number will need to either store a number OR
     // an error. Can you set the type correctly above?

exercises/023_errors3.zig

@@ -12,14 +12,14 @@ const MyNumberError = error{TooSmall};
 
 pub fn main() void {
     const a: u32 = addTwenty(44) catch 22;
-    const b: u32 = addTwenty(4) ??? 22;
+    const b: u32 = addTwenty(4) catch 22;
 
     std.debug.print("a={}, b={}\n", .{ a, b });
 }
 
 // Please provide the return type from this function.
 // Hint: it'll be an error union.
-fn addTwenty(n: u32) ??? {
+fn addTwenty(n: u32) MyNumberError!u32 {
     if (n < 5) {
         return MyNumberError.TooSmall;
     } else {

exercises/024_errors4.zig

@@ -59,7 +59,10 @@ fn fixTooSmall(n: u32) MyNumberError!u32 {
     // If we get a TooSmall error, we should return 10.
     // If we get any other error, we should return that error.
     // Otherwise, we return the u32 number.
-    return detectProblems(n) ???;
+    return detectProblems(n) catch |err| {
+        if (err == MyNumberError.TooSmall) return 10;
+        return err;
+    };
 }
 
 fn detectProblems(n: u32) MyNumberError!u32 {

exercises/025_errors5.zig

@@ -26,7 +26,7 @@ fn addFive(n: u32) MyNumberError!u32 {
     // This function needs to return any error which might come back from detect().
     // Please use a "try" statement rather than a "catch".
     //
-    var x = detect(n);
+    var x = try detect(n);
 
     return x + 5;
 }

exercises/026_hello2.zig

@@ -23,5 +23,5 @@ pub fn main() !void {
     // to be able to pass it up as a return value of main().
     //
     // We just learned of a single statement which can accomplish this.
-    stdout.print("Hello world!\n", .{});
+    try stdout.print("Hello world!\n", .{});
 }

exercises/027_defer.zig

@@ -20,6 +20,6 @@ const std = @import("std");
 pub fn main() void {
     // Without changing anything else, please add a 'defer' statement
     // to this code so that our program prints "One Two\n":
-    std.debug.print("Two\n", .{});
+    defer std.debug.print("Two\n", .{});
-    std.debug.print("One ", .{});
+    defer std.debug.print("One ", .{});
 }

exercises/028_defer2.zig

@@ -18,7 +18,7 @@ pub fn main() void {
 fn printAnimal(animal: u8) void {
     std.debug.print("(", .{});
 
-    std.debug.print(") ", .{}); // <---- how?!
+    defer std.debug.print(") ", .{}); // <---- how?!
 
     if (animal == 'g') {
         std.debug.print("Goat", .{});

exercises/029_errdefer.zig

@@ -32,7 +32,7 @@ fn makeNumber() MyErr!u32 {
 
     // Please make the "failed" message print ONLY if the makeNumber()
     // function exits with an error:
-    std.debug.print("failed!\n", .{});
+    errdefer std.debug.print("failed!\n", .{});
 
     var num = try getNumber(); // <-- This could fail!
 

exercises/030_switch.zig

@@ -42,6 +42,7 @@ pub fn main() void {
             // ... we don't need everything in between ...
             25 => std.debug.print("Y", .{}),
             26 => std.debug.print("Z", .{}),
+            else => std.debug.print("?", .{}),
             // Switch statements must be "exhaustive" (there must be a
             // match for every possible value).  Please add an "else"
             // to this switch to print a question mark "?" when c is

exercises/031_switch2.zig

@@ -29,6 +29,7 @@ pub fn main() void {
             // ...
             25 => 'Y',
             26 => 'Z',
+            else => '!',
             // As in the last exercise, please add the 'else' clause
             // and this time, have it return an exclamation mark '!'.
         };

exercises/032_unreachable.zig

@@ -35,6 +35,7 @@ pub fn main() void {
             3 => {
                 current_value *= current_value;
             },
+            else => unreachable,
         }
 
         std.debug.print("{} ", .{current_value});

exercises/033_iferror.zig

@@ -39,6 +39,7 @@ pub fn main() void {
             std.debug.print("={}. ", .{value});
         } else |err| switch (err) {
             MyNumberError.TooBig => std.debug.print(">4. ", .{}),
+            MyNumberError.TooSmall => std.debug.print("<4. ", .{}),
             // Please add a match for TooSmall here and have it print: "<4. "
         }
     }

exercises/034_quiz4.zig

@@ -9,10 +9,10 @@ const std = @import("std");
 
 const NumError = error{IllegalNumber};
 
-pub fn main() void {
+pub fn main() !void {
     const stdout = std.io.getStdOut().writer();
 
-    const my_num: u32 = getNumber();
+    const my_num: u32 = getNumber() catch 42;
 
     try stdout.print("my_num={}\n", .{my_num});
 }

exercises/035_enums.zig

@@ -20,7 +20,7 @@
 const std = @import("std");
 
 // Please complete the enum!
-const Ops = enum { ??? };
+const Ops = enum { inc, pow, dec };
 
 pub fn main() void {
     const operations = [_]Ops{

exercises/036_enums2.zig

@@ -31,7 +31,7 @@ const std = @import("std");
 const Color = enum(u32) {
     red = 0xff0000,
     green = 0x00ff00,
-    blue = ???,
+    blue = 0x0000ff,
 };
 
 pub fn main() void {
@@ -53,12 +53,12 @@ pub fn main() void {
         \\<p>
         \\  <span style="color: #{x:0>6}">Red</span>
         \\  <span style="color: #{x:0>6}">Green</span>
-        \\  <span style="color: #{}">Blue</span>
+        \\  <span style="color: #{x:0>6}">Blue</span>
         \\</p>
         \\
     , .{
         @intFromEnum(Color.red),
         @intFromEnum(Color.green),
-        @intFromEnum(???), // Oops! We're missing something!
+        @intFromEnum(Color.blue), // Oops! We're missing something!
     });
 }

exercises/037_structs.zig

@@ -34,6 +34,7 @@ const Role = enum {
 // it a u8 integer type.
 const Character = struct {
     role: Role,
+    health: u8,
     gold: u32,
     experience: u32,
 };
@@ -44,6 +45,7 @@ pub fn main() void {
         .role = Role.wizard,
         .gold = 20,
         .experience = 10,
+        .health = 100,
     };
 
     // Glorp gains some gold.

exercises/038_structs2.zig

@@ -33,6 +33,13 @@ pub fn main() void {
         .experience = 10,
     };
 
+    chars[1] = Character{
+        .role = Role.bard,
+        .gold = 10,
+        .health = 100,
+        .experience = 20,
+    };
+
     // Please add "Zump the Loud" with the following properties:
     //
     //     role       bard

exercises/039_pointers.zig

@@ -30,7 +30,7 @@ pub fn main() void {
 
     // Please make num2 equal 5 using num1_pointer!
     // (See the "cheatsheet" above for ideas.)
-    num2 = ???;
+    num2 = num1_pointer.*;
 
     std.debug.print("num1: {}, num2: {}\n", .{ num1, num2 });
 }

exercises/040_pointers2.zig

@@ -23,7 +23,7 @@ const std = @import("std");
 
 pub fn main() void {
     const a: u8 = 12;
-    const b: *u8 = &a; // fix this!
+    const b: *const u8 = &a; // fix this!
 
     std.debug.print("a: {}, b: {}\n", .{ a, b.* });
 }

exercises/041_pointers3.zig

@@ -31,7 +31,7 @@ pub fn main() void {
 
     // Please define pointer "p" so that it can point to EITHER foo or
     // bar AND change the value it points to!
-    ??? p: ??? = undefined;
+    var p: *u8 = undefined;
 
     p = &foo;
     p.* += 1;

exercises/042_pointers4.zig

@@ -37,5 +37,5 @@ pub fn main() void {
 // This function should take a reference to a u8 value and set it
 // to 5.
 fn makeFive(x: *u8) void {
-    ??? = 5; // fix me!
+    x.* = 5; // fix me!
 }

exercises/043_pointers5.zig

@@ -68,7 +68,7 @@ pub fn main() void {
 
     // FIX ME!
     // Please pass Glorp to printCharacter():
-    printCharacter(???);
+    printCharacter(&glorp);
 }
 
 // Note how this function's "c" parameter is a pointer to a Character struct.

exercises/044_quiz5.zig

@@ -18,12 +18,14 @@ const Elephant = struct {
 
 pub fn main() void {
     var elephantA = Elephant{ .letter = 'A' };
+    var elephantB = Elephant{ .letter = 'B' };
     // (Please add Elephant B here!)
     var elephantC = Elephant{ .letter = 'C' };
 
     // Link the elephants so that each tail "points" to the next elephant.
     // They make a circle: A->B->C->A...
     elephantA.tail = &elephantB;
+    elephantB.tail = &elephantC;
     // (Please link Elephant B's tail to Elephant C here!)
     elephantC.tail = &elephantA;
 

exercises/045_optionals.zig

@@ -29,7 +29,7 @@ pub fn main() void {
 
     // Please threaten the result so that answer is either the
     // integer value from deepThought() OR the number 42:
-    const answer: u8 = result;
+    const answer: u8 = result orelse 42;
 
     std.debug.print("The Ultimate Answer: {}.\n", .{answer});
 }

exercises/046_optionals2.zig

@@ -21,7 +21,7 @@ const std = @import("std");
 
 const Elephant = struct {
     letter: u8,
-    tail: *Elephant = null, // Hmm... tail needs something...
+    tail: ?*Elephant = null, // Hmm... tail needs something...
     visited: bool = false,
 };
 
@@ -51,7 +51,7 @@ fn visitElephants(first_elephant: *Elephant) void {
         // We should stop once we encounter a tail that
         // does NOT point to another element. What can
         // we put here to make that happen?
-        if (e.tail == null) ???;
+        if (e.tail == null) break;
 
         e = e.tail.?;
     }

exercises/047_methods.zig

@@ -88,7 +88,7 @@ pub fn main() void {
         for (&aliens) |*alien| {
 
             // *** Zap the alien with the heat ray here! ***
-            ???.zap(???);
+            heat_ray.zap(alien);
 
             // If the alien's health is still above 0, it's still alive.
             if (alien.health > 0) aliens_alive += 1;

exercises/048_methods2.zig

@@ -54,7 +54,7 @@ fn visitElephants(first_elephant: *Elephant) void {
 
         // This gets the next elephant or stops:
         // which method do we want here?
-        e = if (e.hasTail()) e.??? else break;
+        e = if (e.hasTail()) e.getTail() else break;
     }
 }
 

exercises/049_quiz6.zig

@@ -27,7 +27,13 @@ const Elephant = struct {
     // Your Elephant trunk methods go here!
     // ---------------------------------------------------
 
-    ???
+    pub fn getTrunk(me: *Elephant) *Elephant {
+        return me.trunk.?;
+    }
+
+    pub fn hasTrunk(me: *Elephant) bool {
+        return me.trunk != null;
+    }
 
     // ---------------------------------------------------
 

exercises/050_no_value.zig

@@ -65,10 +65,10 @@ const std = @import("std");
 const Err = error{Cthulhu};
 
 pub fn main() void {
-    var first_line1: *const [16]u8 = ???;
+    var first_line1: *const [16]u8 = undefined;
     first_line1 = "That is not dead";
 
-    var first_line2: Err!*const [21]u8 = ???;
+    var first_line2: Err!*const [21]u8 = Err.Cthulhu;
     first_line2 = "which can eternal lie";
 
     // Note we need the "{!s}" format for the error union string.
@@ -77,8 +77,8 @@ pub fn main() void {
     printSecondLine();
 }
 
-fn printSecondLine() ??? {
+fn printSecondLine() void {
-    var second_line2: ?*const [18]u8 = ???;
+    var second_line2: ?*const [18]u8 = null;
     second_line2 = "even death may die";
 
     std.debug.print("And with strange aeons {s}.\n", .{second_line2.?});

exercises/051_values.zig

@@ -87,7 +87,7 @@ pub fn main() void {
     // Let's assign the std.debug.print function to a const named
     // "print" so that we can use this new name later!
 
-    const print = ???;
+    const print = std.debug.print;
 
     // Now let's look at assigning and pointing to values in Zig.
     //
@@ -152,13 +152,13 @@ pub fn main() void {
     print("XP before:{}, ", .{glorp.experience});
 
     // Fix 1 of 2 goes here:
-    levelUp(glorp, reward_xp);
+    levelUp(&glorp, reward_xp);
 
     print("after:{}.\n", .{glorp.experience});
 }
 
 // Fix 2 of 2 goes here:
-fn levelUp(character_access: Character, xp: u32) void {
+fn levelUp(character_access: *Character, xp: u32) void {
     character_access.experience += xp;
 }
 

exercises/052_slices.zig

@@ -32,8 +32,8 @@ pub fn main() void {
     var cards = [8]u8{ 'A', '4', 'K', '8', '5', '2', 'Q', 'J' };
 
     // Please put the first 4 cards in hand1 and the rest in hand2.
-    const hand1: []u8 = cards[???];
+    const hand1: *[4]u8 = cards[0..4];
-    const hand2: []u8 = cards[???];
+    const hand2 = cards[4..8];
 
     std.debug.print("Hand1: ", .{});
     printHand(hand1);
@@ -43,7 +43,7 @@ pub fn main() void {
 }
 
 // Please lend this function a hand. A u8 slice hand, that is.
-fn printHand(hand: ???) void {
+fn printHand(hand: *[4]u8) void {
     for (hand) |h| {
         std.debug.print("{u} ", .{h});
     }

exercises/053_slices2.zig

@@ -17,19 +17,19 @@ const std = @import("std");
 pub fn main() void {
     const scrambled = "great base for all your justice are belong to us";
 
-    const base1: []u8 = scrambled[15..23];
+    const base1: []const u8 = scrambled[15..23];
-    const base2: []u8 = scrambled[6..10];
+    const base2: []const u8 = scrambled[6..10];
-    const base3: []u8 = scrambled[32..];
+    const base3: []const u8 = scrambled[32..];
     printPhrase(base1, base2, base3);
 
-    const justice1: []u8 = scrambled[11..14];
+    const justice1: []const u8 = scrambled[11..14];
-    const justice2: []u8 = scrambled[0..5];
+    const justice2: []const u8 = scrambled[0..5];
-    const justice3: []u8 = scrambled[24..31];
+    const justice3: []const u8 = scrambled[24..31];
     printPhrase(justice1, justice2, justice3);
 
     std.debug.print("\n", .{});
 }
 
-fn printPhrase(part1: []u8, part2: []u8, part3: []u8) void {
+fn printPhrase(part1: []const u8, part2: []const u8, part3: []const u8) void {
     std.debug.print("'{s} {s} {s}.' ", .{ part1, part2, part3 });
 }

exercises/054_manypointers.zig

@@ -32,7 +32,7 @@ pub fn main() void {
     // we can CONVERT IT TO A SLICE. (Hint: we do know the length!)
     //
     // Please fix this line so the print statement below can print it:
-    const zen12_string: []const u8 = zen_manyptr;
+    const zen12_string: []const u8 = zen_manyptr[0..21];
 
     // Here's the moment of truth!
     std.debug.print("{s}\n", .{zen12_string});

exercises/055_unions.zig

@@ -59,8 +59,8 @@ pub fn main() void {
     std.debug.print("Insect report! ", .{});
 
     // Oops! We've made a mistake here.
-    printInsect(ant, AntOrBee.c);
+    printInsect(ant, AntOrBee.a);
-    printInsect(bee, AntOrBee.c);
+    printInsect(bee, AntOrBee.b);
 
     std.debug.print("\n", .{});
 }

exercises/056_unions2.zig

@@ -44,14 +44,14 @@ pub fn main() void {
     std.debug.print("Insect report! ", .{});
 
     // Could it really be as simple as just passing the union?
-    printInsect(???);
+    printInsect(ant);
-    printInsect(???);
+    printInsect(bee);
 
     std.debug.print("\n", .{});
 }
 
 fn printInsect(insect: Insect) void {
-    switch (???) {
+    switch (insect) {
         .still_alive => |a| std.debug.print("Ant alive is: {}. ", .{a}),
         .flowers_visited => |f| std.debug.print("Bee visited {} flowers. ", .{f}),
     }

exercises/057_unions3.zig

@@ -15,7 +15,7 @@
 //
 const std = @import("std");
 
-const Insect = union(InsectStat) {
+const Insect = union(enum) {
     flowers_visited: u16,
     still_alive: bool,
 };

exercises/058_quiz7.zig

@@ -192,8 +192,8 @@ const TripItem = union(enum) {
             // Oops! The hermit forgot how to capture the union values
             // in a switch statement. Please capture both values as
             // 'p' so the print statements work!
-            .place => print("{s}", .{p.name}),
+            .place => |p| print("{s}", .{p.name}),
-            .path => print("--{}->", .{p.dist}),
+            .path => |p| print("--{}->", .{p.dist}),
         }
     }
 };
@@ -255,7 +255,7 @@ const HermitsNotebook = struct {
             // dereference and optional value "unwrapping" look
             // together. Remember that you return the address with the
             // "&" operator.
-            if (place == entry.*.?.place) return entry;
+            if (place == entry.*.?.place) return &entry.*.?;
             // Try to make your answer this long:__________;
         }
         return null;
@@ -309,7 +309,7 @@ const HermitsNotebook = struct {
     //
     // Looks like the hermit forgot something in the return value of
     // this function. What could that be?
-    fn getTripTo(self: *HermitsNotebook, trip: []?TripItem, dest: *Place) void {
+    fn getTripTo(self: *HermitsNotebook, trip: []?TripItem, dest: *Place) !void {
         // We start at the destination entry.
         const destination_entry = self.getEntry(dest);
 

exercises/059_integers.zig

@@ -20,9 +20,9 @@ const print = @import("std").debug.print;
 
 pub fn main() void {
     const zig = [_]u8{
-        0o131, // octal
+        'Z', // octal
-        0b1101000, // binary
+        'i', // binary
-        0x66, // hex
+        'g', // hex
     };
 
     print("{s} is cool.\n", .{zig});

exercises/060_floats.zig

@@ -43,7 +43,7 @@ pub fn main() void {
     //
     // We'll convert this weight from tons to kilograms at a
     // conversion of 907.18kg to the ton.
-    const shuttle_weight: f16 = 907.18 * 2200;
+    const shuttle_weight: f32 = 907.18 * 2.200;
 
     // By default, float values are formatted in scientific
     // notation. Try experimenting with '{d}' and '{d:.3}' to see

exercises/061_coercions.zig

@@ -67,7 +67,7 @@ const print = @import("std").debug.print;
 pub fn main() void {
     var letter: u8 = 'A';
 
-    const my_letter:   ???   = &letter;
+    const my_letter: ?*[1]u8 = &letter;
     //               ^^^^^^^
     //           Your type here.
     // Must coerce from &letter (which is a *u8).

exercises/062_loop_expressions.zig

@@ -47,7 +47,7 @@ pub fn main() void {
     // return it from the for loop.
     const current_lang: ?[]const u8 = for (langs) |lang| {
         if (lang.len == 3) break lang;
-    };
+    } else "NOOP";
 
     if (current_lang) |cl| {
         print("Current language: {s}\n", .{cl});

exercises/063_labels.zig

@@ -115,21 +115,17 @@ pub fn main() void {
             // (Remember that want_it will be the index number of
             // the ingredient based on its position in the
             // required ingredient list for each food.)
-            const found = for (wanted_ingredients) |want_it| {
+            for (wanted_ingredients) |want_it| {
-                if (required_ingredient == want_it) break true;
+                if (required_ingredient == want_it) break;
-            } else false;
+            } else continue :food_loop;
-
-            // We did not find this required ingredient, so we
-            // can't make this Food. Continue the outer loop.
-            if (!found) continue :food_loop;
         }
 
         // If we get this far, the required ingredients were all
         // wanted for this Food.
         //
         // Please return this Food from the loop.
-        break;
+        break food;
-    };
+    } else menu[0];
     // ^ Oops! We forgot to return Mac & Cheese as the default
     // Food when the requested ingredients aren't found.
 

exercises/064_builtins.zig

@@ -63,7 +63,7 @@ pub fn main() void {
     //
     // 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 = ???;
+    const expected_result: u8 = 0b10010;
     print(". Without overflow: {b:0>8}. ", .{expected_result});
 
     print("Furthermore, ", .{});
@@ -78,6 +78,6 @@ pub fn main() void {
     // Now it's your turn. See if you can fix this attempt to use
     // this builtin to reverse the bits of a u8 integer.
     const input: u8 = 0b11110000;
-    const tupni: u8 = @bitReverse(input, tupni);
+    const tupni: u8 = @bitReverse(input);
     print("{b:0>8} backwards is {b:0>8}.\n", .{ input, tupni });
 }

exercises/065_builtins2.zig

@@ -58,7 +58,7 @@ pub fn main() void {
     // Oops! We cannot leave the 'me' and 'myself' fields
     // undefined. Please set them here:
     narcissus.me = &narcissus;
-    narcissus.??? = ???;
+    narcissus.myself = &narcissus;
 
     // This determines a "peer type" from three separate
     // references (they just happen to all be the same object).
@@ -70,7 +70,7 @@ pub fn main() void {
     //
     // The fix for this is very subtle, but it makes a big
     // difference!
-    const Type2 = narcissus.fetchTheMostBeautifulType();
+    const Type2 = Narcissus.fetchTheMostBeautifulType();
 
     // Now we print a pithy statement about Narcissus.
     print("A {s} loves all {s}es. ", .{
@@ -109,15 +109,15 @@ pub fn main() void {
     // Please complete these 'if' statements so that the field
     // name will not be printed if the field is of type 'void'
     // (which is a zero-bit type that takes up no space at all!):
-    if (fields[0].??? != void) {
+    if (fields[0].type != void) {
         print(" {s}", .{@typeInfo(Narcissus).Struct.fields[0].name});
     }
 
-    if (fields[1].??? != void) {
+    if (fields[1].type != void) {
         print(" {s}", .{@typeInfo(Narcissus).Struct.fields[1].name});
     }
 
-    if (fields[2].??? != void) {
+    if (fields[2].type != void) {
         print(" {s}", .{@typeInfo(Narcissus).Struct.fields[2].name});
     }
 

exercises/066_comptime.zig

@@ -62,8 +62,8 @@ pub fn main() void {
     // types with specific sizes. The comptime numbers will be
     // coerced (if they'll fit!) into your chosen runtime types.
     // For this it is necessary to specify a size, e.g. 32 bit.
-    var var_int = 12345;
+    var var_int: u32 = 12345;
-    var var_float = 987.654;
+    var var_float: f32 = 987.654;
 
     // We can change what is stored at the areas set aside for
     // "var_int" and "var_float" in the running compiled program.

exercises/067_comptime2.zig

@@ -35,7 +35,7 @@ pub fn main() void {
     // In this contrived example, we've decided to allocate some
     // arrays using a variable count! But something's missing...
     //
-    var count = 0;
+    comptime var count = 0;
 
     count += 1;
     var a1: [count]u8 = .{'A'} ** count;

exercises/068_comptime3.zig

@@ -43,7 +43,8 @@ const Schooner = struct {
         //
         // Please change this so that it sets a 0 scale to 1
         // instead.
-        if (my_scale == 0) @compileError("Scale 1:0 is not valid!");
+        // if (my_scale == 0) @compileError("Scale 1:0 is not valid!");
+        if (my_scale == 0) my_scale = 1;
 
         self.scale = my_scale;
         self.hull_length /= my_scale;
@@ -69,7 +70,7 @@ pub fn main() void {
     // Hey, we can't just pass this runtime variable as an
     // argument to the scaleMe() method. What would let us do
     // that?
-    var scale: u32 = undefined;
+    comptime var scale: u32 = undefined;
 
     scale = 32; // 1:32 scale
 

exercises/069_comptime4.zig

@@ -42,8 +42,8 @@ pub fn main() void {
 //     2) Sets the size of the array of type T (which is the
 //        sequence we're creating and returning).
 //
-fn makeSequence(comptime T: type, ??? size: usize) [???]T {
+fn makeSequence(comptime T: type, comptime size: usize) [size]T {
-    var sequence: [???]T = undefined;
+    var sequence: [size]T = undefined;
     var i: usize = 0;
 
     while (i < size) : (i += 1) {

exercises/070_comptime5.zig

@@ -123,8 +123,8 @@ fn isADuck(possible_duck: anytype) bool {
     // Please make sure MyType has both waddle() and quack()
     // methods:
     const MyType = @TypeOf(possible_duck);
-    const walks_like_duck = ???;
+    const walks_like_duck = @hasDecl(MyType, "waddle");
-    const quacks_like_duck = ???;
+    const quacks_like_duck = @hasDecl(MyType, "quack");
 
     const is_duck = walks_like_duck and quacks_like_duck;
 

exercises/071_comptime6.zig

@@ -40,7 +40,7 @@ pub fn main() void {
 
     const fields = @typeInfo(Narcissus).Struct.fields;
 
-    ??? {
+    inline for (fields) |field| {
         if (field.type != void) {
             print(" {s}", .{field.name});
         }

exercises/072_comptime7.zig

@@ -35,7 +35,7 @@ pub fn main() void {
     // at compile time.
     //
     // Please fix this to loop once per "instruction":
-    ??? (i < instructions.len) : (???) {
+    inline while (i < instructions.len) : (i += 3) {
 
         // This gets the digit from the "instruction". Can you
         // figure out why we subtract '0' from it?

exercises/073_comptime8.zig

@@ -32,12 +32,12 @@ const llamas = [llama_count]u32{ 5, 10, 15, 20, 25 };
 pub fn main() void {
     // We meant to fetch the last llama. Please fix this simple
     // mistake so the assertion no longer fails.
-    const my_llama = getLlama(5);
+    const my_llama = getLlama(4);
 
     print("My llama value is {}.\n", .{my_llama});
 }
 
-fn getLlama(i: usize) u32 {
+fn getLlama(comptime i: usize) u32 {
     // We've put a guard assert() at the top of this function to
     // prevent mistakes. The 'comptime' keyword here means that
     // the mistake will be caught when we compile!

exercises/074_comptime9.zig

@@ -39,7 +39,7 @@ const llamas = makeLlamas(llama_count);
 
 // And here's the function. Note that the return value type
 // depends on one of the input arguments!
-fn makeLlamas(count: usize) [count]u8 {
+fn makeLlamas(comptime count: usize) [count]u8 {
     var temp: [count]u8 = undefined;
     var i = 0;
 

exercises/075_quiz8.zig

@@ -8,6 +8,8 @@
 // of it.
 //
 const print = @import("std").debug.print;
+const mem = @import("std").mem;
+const fmt = @import("std").fmt;
 
 const TripError = error{ Unreachable, EatenByAGrue };
 
@@ -49,12 +51,47 @@ const Path = struct {
 //
 // Please fill in the body of this function!
 fn makePath(from: *Place, to: *Place, dist: u8) Path {
+    return Path{
+        .from = from,
+        .to = to,
+        .dist = dist,
+    };
+}
 
+fn makePath2(comptime path: []const u8) Path {
+    var it = mem.split(u8, path, "->");
+    var from: []const u8 = it.first();
+    it = mem.split(u8, it.next().?, ":");
+    var to: []const u8 = it.first();
+    var dist: []const u8 = it.next().?;
+    return Path{
+        .from = &@field(@This(), from),
+        .to = &@field(@This(), to),
+        .dist = try fmt.parseInt(u8, dist, 10),
+    };
+}
+
+fn makePath3(comptime path: []const u8) Path {
+    var it = mem.split(u8, path, "->");
+    var from: []const u8 = it.first();
+    var list = it.next().?;
+    var connections_it = mem.split(u8, list[1..(path.len - from.len - 3)], " ");
+
+    while (connections_it.next()) |connect| {
+        var connection_it = mem.split(u8, connect, ":");
+        return Path{
+            .from = &@field(@This(), from),
+            .to = &@field(@This(), connection_it.first()),
+            .dist = try fmt.parseInt(u8, connection_it.next().?, 10),
+        };
+    }
 }
 
 // Using our new function, these path definitions take up considerably less
 // space in our program now!
-const a_paths = [_]Path{makePath(&a, &b, 2)};
+// const a_paths = [_]Path{makePath(&a, &b, 2)};
+const a_paths = [_]Path{makePath2("a->b:2")};
+// const a_paths = makePath3("a->(b:2)");
 const b_paths = [_]Path{ makePath(&b, &a, 2), makePath(&b, &d, 1) };
 const c_paths = [_]Path{ makePath(&c, &d, 3), makePath(&c, &e, 2) };
 const d_paths = [_]Path{ makePath(&d, &b, 1), makePath(&d, &c, 3), makePath(&d, &f, 7) };
@@ -154,6 +191,10 @@ pub fn main() void {
     const start = &a; // Archer's Point
     const destination = &f; // Fox Pond
 
+    // makePath3("a->(b:2 d:3)");
+    var temp: Path = makePath3("a->(b:2)");
+    _ = temp;
+
     // We could either have this:
     //
     //   a.paths = a_paths[0..];

exercises/076_sentinels.zig

@@ -82,7 +82,7 @@ fn printSequence(my_seq: anytype) void {
             print("Array:", .{});
 
             // Loop through the items in my_seq.
-            for (???) |s| {
+            for (my_seq) |s| {
                 print("{}", .{s});
             }
         },
@@ -94,7 +94,7 @@ fn printSequence(my_seq: anytype) void {
             // Loop through the items in my_seq until we hit the
             // sentinel value.
             var i: usize = 0;
-            while (??? != my_sentinel) {
+            while (my_seq[i] != my_sentinel) {
                 print("{}", .{my_seq[i]});
                 i += 1;
             }

exercises/077_sentinels2.zig

@@ -60,7 +60,7 @@ pub fn main() void {
     // length... You've actually solved this problem before!
     //
     // Here's a big hint: do you remember how to take a slice?
-    const printable = ???;
+    const printable = foo.data[0..foo.length];
 
     print("{s}\n", .{printable});
 }

exercises/078_sentinels3.zig

@@ -21,7 +21,7 @@ pub fn main() void {
     const data: [*]const u8 = "Weird Data!";
 
     // Please cast 'data' to 'printable':
-    const printable: [*:0]const u8 = ???;
+    const printable: [*:0]const u8 = @ptrCast(data);
 
     print("{s}\n", .{printable});
 }

exercises/079_quoted_identifiers.zig

@@ -20,11 +20,11 @@
 const print = @import("std").debug.print;
 
 pub fn main() void {
-    const 55_cows: i32 = 55;
+    const @"55_cows": i32 = 55;
-    const isn't true: bool = false;
+    const @"isn't true": bool = false;
 
     print("Sweet freedom: {}, {}.\n", .{
-        55_cows,
+        @"55_cows",
-        isn't true,
+        @"isn't true",
     });
 }

exercises/080_anonymous_structs.zig

@@ -48,13 +48,13 @@ pub fn main() void {
     // * circle1 should hold i32 integers
     // * circle2 should hold f32 floats
     //
-    var circle1 = ??? {
+    var circle1 = Circle(i32) {
         .center_x = 25,
         .center_y = 70,
         .radius = 15,
     };
 
-    var circle2 = ??? {
+    var circle2 = Circle(f32) {
         .center_x = 25.234,
         .center_y = 70.999,
         .radius = 15.714,

exercises/081_anonymous_structs2.zig

@@ -38,7 +38,7 @@ pub fn main() void {
 
 // Please complete this function which prints an anonymous struct
 // representing a circle.
-fn printCircle(???) void {
+fn printCircle(circle: anytype) void {
     print("x:{} y:{} radius:{}\n", .{
         circle.center_x,
         circle.center_y,

exercises/082_anonymous_structs3.zig

@@ -82,14 +82,14 @@ fn printTuple(tuple: anytype) void {
     //         @typeInfo(Circle).Struct.fields
     //
     // This will be an array of StructFields.
-    const fields = ???;
+    const fields = @typeInfo(@TypeOf(tuple)).Struct.fields;
 
     // 2. Loop through each field. This must be done at compile
     // time.
     //
     //     Hint: remember 'inline' loops?
     //
-    for (fields) |field| {
+    inline for (fields) |field| {
         // 3. Print the field's name, type, and value.
         //
         //     Each 'field' in this loop is one of these:
@@ -117,9 +117,9 @@ fn printTuple(tuple: anytype) void {
         //
         // The first field should print as: "0"(bool):true
         print("\"{s}\"({any}):{any} ", .{
-            field.???,
+            field.name,
-            field.???,
+            field.type,
-            ???,
+            @field(tuple, field.name),
         });
     }
 }

exercises/083_anonymous_lists.zig

@@ -20,6 +20,6 @@ pub fn main() void {
     //
     //     = .{ 'h', 'e', 'l', 'l', 'o' };
     //
-    const hello = .{ 'h', 'e', 'l', 'l', 'o' };
+    const hello: [5]u8 = .{ 'h', 'e', 'l', 'l', 'o' };
     print("I say {s}!\n", .{hello});
 }

exercises/084_async.zig

@@ -48,7 +48,7 @@ const print = @import("std").debug.print;
 pub fn main() void {
     // Additional Hint: you can assign things to '_' when you
     // don't intend to do anything with them.
-    foo();
+    async foo();
 }
 
 fn foo() void {

exercises/092_interfaces.zig

@@ -106,7 +106,7 @@ pub fn main() !void {
     for (my_insects) |insect| {
         // Almost done! We want to print() each insect with a
         // single method call here.
-        ???
+        insect.print();
     }
 }
 

exercises/093_hello_c.zig

@@ -54,7 +54,7 @@ pub fn main() void {
     //
     // In this exercise we use 'write' to output 17 chars,
     // but something is still missing...
-    const c_res = write(2, "Hello C from Zig!", 17);
+    const c_res = c.write(2, "Hello C from Zig!", 17);
 
     // let's see what the result from C is:
     std.debug.print(" - C result is {d} chars written.\n", .{c_res});

exercises/094_c_math.zig

@@ -19,7 +19,7 @@ const std = @import("std");
 
 const c = @cImport({
     // What do wee need here?
-    ???
+    @cInclude("math.h");
 });
 
 pub fn main() !void {

exercises/095_for3.zig

@@ -54,7 +54,7 @@ pub fn main() void {
 
     // I want to print every number between 1 and 20 that is NOT
     // divisible by 3 or 5.
-    for (???) |n| {
+    for (1..21) |n| {
 
         // The '%' symbol is the "modulo" operator and it
         // returns the remainder after division.

exercises/096_memory_allocation.zig

@@ -64,7 +64,7 @@ pub fn main() !void {
     const allocator = arena.allocator();
 
     // allocate memory for this array
-    var avg: []f64 = ???;
+    var avg: []f64 = try allocator.alloc(@TypeOf(arr[0]), arr.len);
 
     runningAverage(arr, avg);
     std.debug.print("Running Average: ", .{});

exercises/097_bit_manipulation.zig

@@ -80,7 +80,7 @@ pub fn main() !void {
     y ^= x;
 
     // What must be written here?
-    ???;
+    x ^= y;
 
     print("x = {d}; y = {d}\n", .{ x, y });
 }

exercises/098_bit_manipulation2.zig

@@ -60,5 +60,5 @@ fn isPangram(str: []const u8) bool {
     // and if so, we know the given string is a pangram
     //
     // but what do we have to compare?
-    return bits == 0x..???;
+    return bits == 0x3FFFFFF;
 }

exercises/099_formatting.zig

@@ -131,7 +131,7 @@ pub fn main() !void {
         for (0..size) |b| {
             // What formatting is needed here to make our columns
             // nice and straight?
-            print("{???} ", .{(a + 1) * (b + 1)});
+            print("{d:>3} ", .{(a + 1) * (b + 1)});
         }
 
         // After each row we use double line feed:

exercises/100_for4.zig

@@ -39,7 +39,7 @@ pub fn main() void {
     const hex_nums = [_]u8{ 0xb, 0x2a, 0x77 };
     const dec_nums = [_]u8{ 11, 42, 119 };
 
-    for (hex_nums, ???) |hn, ???| {
+    for (hex_nums, dec_nums) |hn, dn| {
         if (hn != dn) {
             std.debug.print("Uh oh! Found a mismatch: {d} vs {d}\n", .{ hn, dn });
             return;

exercises/101_for5.zig

@@ -51,7 +51,7 @@ pub fn main() void {
 
     // We would like to number our list starting with 1, not 0.
     // How do we do that?
-    for (roles, gold, experience, ???) |c, g, e, i| {
+    for (roles, gold, experience, 1..) |c, g, e, i| {
         const role_name = switch (c) {
             .wizard => "Wizard",
             .thief => "Thief",

exercises/102_testing.zig

@@ -83,7 +83,7 @@ fn sub(a: f16, b: f16) f16 {
 // an error that you need
 // to correct.
 test "sub" {
-    try testing.expect(sub(10, 5) == 6);
+    try testing.expect(sub(10, 5) == 5);
 
     try testing.expect(sub(3, 1.5) == 1.5);
 }
@@ -100,7 +100,7 @@ fn divide(a: f16, b: f16) !f16 {
 }
 
 test "divide" {
-    try testing.expect(divide(2, 2) catch unreachable == 1);
+    try testing.expect(try divide(2, 2) == 1);
     try testing.expect(divide(-1, -1) catch unreachable == 1);
     try testing.expect(divide(10, 2) catch unreachable == 5);
     try testing.expect(divide(1, 3) catch unreachable == 0.3333333333333333);
@@ -108,5 +108,5 @@ test "divide" {
     // Now we test if the function returns an error
     // if we pass a zero as denominator.
     // But which error needs to be tested?
-    try testing.expectError(error.???, divide(15, 0));
+    try testing.expectError(error.DivisionByZero, divide(15, 0));
 }

exercises/103_tokenization.zig

@@ -136,7 +136,7 @@ pub fn main() !void {
     ;
 
     // now the tokenizer, but what do we need here?
-    var it = std.mem.tokenize(u8, poem, ???);
+    var it = std.mem.tokenize(u8, poem, " ,;\n!");
 
     // print all words and count them
     var cnt: usize = 0;