feat(Week05): Add exercises and solutions

1 files changed, 23 insertions, 0 deletions

diff --git a/Week05/Exercise20.cpp b/Week05/Exercise20.cpp
new file mode 100644
index 0000000..b44c0b3
--- /dev/null
+++ b/Week05/Exercise20.cpp
@@ -0,0 +1,23 @@
+#include <iostream>
+
+int main() {
+    unsigned int number;
+    std::cin >> number;
+
+    unsigned int check_digit = number % 10;
+    number /= 10;
+
+    unsigned int sum = 0, digit = 0;
+    for (unsigned int multiplier = 2; number != 0; multiplier = multiplier % 2 + 1, number /= 10) {
+        digit = (number % 10) * multiplier;
+        if (digit > 9) digit -= 9;
+        sum += digit;
+    }
+
+    if ((10 - (sum % 10)) % 10 == check_digit)
+        std::cout << "Valid" << std::endl;
+    else
+        std::cout << "Invalid" << std::endl;
+
+    return 0;
+}