Add 2021 day 8 puzzles

Part two needs a tidy-up which will come in a bit.

But this is how I got the correct answer.

2021/puzzle-08-01.cc

@@ -0,0 +1,32 @@
+//
+// Created by Matthew Gretton-Dann on 08/12/2021.
+//
+
+#include <iostream>
+#include <string>
+
+auto main() -> int
+{
+  std::string line;
+  unsigned count{0};
+  while (std::getline(std::cin, line)) {
+    line = line.substr(line.find('|') + 1);
+    unsigned this_digit{0};
+    for (auto c : line) {
+      if (c == ' ') {
+        if (this_digit == 2 || this_digit == 3 || this_digit == 4 || this_digit == 7) {
+          ++count;
+        }
+        this_digit = 0;
+      }
+      else {
+        ++this_digit;
+      }
+    }
+    if (this_digit == 2 || this_digit == 3 || this_digit == 4 || this_digit == 7) {
+      ++count;
+    }
+  }
+  std::cout << "Simple digits: " << count << '\n';
+  return 0;
+}