Added day26 solution

Author: avidLearnerInProgress

30-days-of-code-july/26.addDigits.cpp

@@ -0,0 +1,11 @@
+class Solution {
+public:
+    int addDigits(int num) {
+        int mod = num%9;
+        if(num==0)
+            return 0;
+        if(mod==0)
+            return 9;
+        return mod;
+    }
+};``