Added CC_Validator code

cc_validator.cpp

@@ -0,0 +1,64 @@
+#include <stdio.h>
+#include <iostream>
+#include <string>
+
+using namespace std;
+
+bool isNumberString(const string &s)
+{
+    int len = s.length();
+    for (int i = 0; i < len; i++)
+    {
+        if (s[i] < '0' || s[i] > '9')
+            return false;
+    }
+    return true;
+}
+
+int main()
+{
+    string ccNumber;
+
+    cout << "This program uses the Luhn Algorigthm to validate a CC number." << endl;
+    cout << "You can enter 'exit' anytime to quit." << endl;
+
+    while (true)
+    {
+
+        cout << "Please enter a CC number to validate: ";
+        cin >> ccNumber;
+
+        if (ccNumber == "exit")
+            break;
+
+        else if (!isNumberString(ccNumber))
+        {
+            cout << "Bad input! ";
+            continue;
+        }
+
+        int len = ccNumber.length();
+        int doubleEvenSum = 0;
+
+        for (int i = len - 2; i >= 0; i = i - 2)
+        {
+            int dbl = ((ccNumber[i] - 48) * 2);
+            if (dbl > 9)
+            {
+                dbl = (dbl / 10) + (dbl % 10);
+            }
+            doubleEvenSum += dbl;
+        }
+
+        for (int i = len - 1; i >= 0; i = i - 2)
+        {
+            doubleEvenSum += (ccNumber[i] - 48);
+        }
+
+        cout << (doubleEvenSum % 10 == 0 ? "Valid!" : "Invalid!") << endl;
+
+        continue;
+    }
+
+    return 0;
+}