use const for variables that are never modified

exercises/021_errors.zig

@@ -16,7 +16,7 @@ const MyNumberError = error{
 const std = @import("std");
 
 pub fn main() void {
-    var nums = [_]u8{ 2, 3, 4, 5, 6 };
+    const nums = [_]u8{ 2, 3, 4, 5, 6 };
 
     for (nums) |n| {
         std.debug.print("{}", .{n});

exercises/031_switch2.zig

@@ -15,7 +15,7 @@ pub fn main() void {
     const lang_chars = [_]u8{ 26, 9, 7, 42 };
 
     for (lang_chars) |c| {
-        var real_char: u8 = switch (c) {
+        const real_char: u8 = switch (c) {
             1 => 'A',
             2 => 'B',
             3 => 'C',

exercises/033_iferror.zig

@@ -29,12 +29,12 @@ const MyNumberError = error{
 const std = @import("std");
 
 pub fn main() void {
-    var nums = [_]u8{ 2, 3, 4, 5, 6 };
+    const nums = [_]u8{ 2, 3, 4, 5, 6 };
 
     for (nums) |num| {
         std.debug.print("{}", .{num});
 
-        var n = numberMaybeFail(num);
+        const n = numberMaybeFail(num);
         if (n) |value| {
             std.debug.print("={}. ", .{value});
         } else |err| switch (err) {

exercises/063_labels.zig

@@ -103,7 +103,7 @@ pub fn main() void {
     const wanted_ingredients = [_]u8{ 0, 3 }; // Chili, Cheese
 
     // Look at each Food on the menu...
-    var meal = food_loop: for (menu) |food| {
+    const meal = food_loop: for (menu) |food| {
 
         // Now look at each required ingredient for the Food...
         for (food.requires) |required, required_ingredient| {
@@ -115,7 +115,7 @@ 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.)
-            var found = for (wanted_ingredients) |want_it| {
+            const found = for (wanted_ingredients) |want_it| {
                 if (required_ingredient == want_it) break true;
             } else false;