code: add difference

main.cpp

@@ -7,5 +7,6 @@ int main()
     cout << "Enter A and B: ";
     int a, b;
     cin >> a >> b;
-    cout << "A + B = " << a + b << '\n';
+    cout << "A + B = " << a + b << '\n'
+         << "A - B = " << a - b << '\n';
 }