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Diffstat (limited to 'exercises/063_labels.zig')
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diff --git a/exercises/063_labels.zig b/exercises/063_labels.zig new file mode 100644 index 0000000..cdde229 --- /dev/null +++ b/exercises/063_labels.zig @@ -0,0 +1,140 @@ +// +// Loop bodies are blocks, which are also expressions. We've seen +// how they can be used to evaluate and return values. To further +// expand on this concept, it turns out we can also give names to +// blocks by applying a 'label': +// +// my_label: { ... } +// +// Once you give a block a label, you can use 'break' to exit +// from that block. +// +// outer_block: { // outer block +// while (true) { // inner block +// break :outer_block; +// } +// unreachable; +// } +// +// As we've just learned, you can return a value using a break +// statement. Does that mean you can return a value from any +// labeled block? Yes it does! +// +// const foo = make_five: { +// const five = 1 + 1 + 1 + 1 + 1; +// break :make_five five; +// }; +// +// Labels can also be used with loops. Being able to break out of +// nested loops at a specific level is one of those things that +// you won't use every day, but when the time comes, it's +// incredibly convenient. Being able to return a value from an +// inner loop is sometimes so handy, it almost feels like cheating +// (and can help you avoid creating a lot of temporary variables). +// +// const bar: u8 = two_loop: while (true) { +// while (true) { +// break :two_loop 2; +// } +// } else 0; +// +// In the above example, the break exits from the outer loop +// labeled "two_loop" and returns the value 2. The else clause is +// attached to the outer two_loop and would be evaluated if the +// loop somehow ended without the break having been called. +// +// Finally, you can also use block labels with the 'continue' +// statement: +// +// my_while: while (true) { +// continue :my_while; +// } +// +const print = @import("std").debug.print; + +// As mentioned before, we'll soon understand why these two +// numbers don't need explicit types. Hang in there! +const ingredients = 4; +const foods = 4; + +const Food = struct { + name: []const u8, + requires: [ingredients]bool, +}; + +// Chili Macaroni Tomato Sauce Cheese +// ------------------------------------------------------ +// Mac & Cheese x x +// Chili Mac x x +// Pasta x x +// Cheesy Chili x x +// ------------------------------------------------------ + +const menu: [foods]Food = [_]Food{ + Food{ + .name = "Mac & Cheese", + .requires = [ingredients]bool{ false, true, false, true }, + }, + Food{ + .name = "Chili Mac", + .requires = [ingredients]bool{ true, true, false, false }, + }, + Food{ + .name = "Pasta", + .requires = [ingredients]bool{ false, true, true, false }, + }, + Food{ + .name = "Cheesy Chili", + .requires = [ingredients]bool{ true, false, false, true }, + }, +}; + +pub fn main() void { + // Welcome to Cafeteria USA! Choose your favorite ingredients + // and we'll produce a delicious meal. + // + // Cafeteria Customer Note: Not all ingredient combinations + // make a meal. The default meal is macaroni and cheese. + // + // Software Developer Note: Hard-coding the ingredient + // numbers (based on array position) will be fine for our + // tiny example, but it would be downright criminal in a real + // application! + const wanted_ingredients = [_]u8{ 0, 3 }; // Chili, Cheese + + // Look at each Food on the menu... + var meal = food_loop: for (menu) |food| { + + // Now look at each required ingredient for the Food... + for (food.requires) |required, required_ingredient| { + + // This ingredient isn't required, so skip it. + if (!required) continue; + + // See if the customer wanted this ingredient. + // (Remember that want_it will be the index number of + // the ingredient based on its position in the + // required ingredient list for each food.) + var found = for (wanted_ingredients) |want_it| { + if (required_ingredient == want_it) break true; + } else false; + + // 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; + }; + // ^ Oops! We forgot to return Mac & Cheese as the default + // Food when the requested ingredients aren't found. + + print("Enjoy your {s}!\n", .{meal.name}); +} + +// Challenge: You can also do away with the 'found' variable in +// the inner loop. See if you can figure out how to do that! |