add cirtical situation

clang.md

@@ -452,6 +452,15 @@ int main() {
 
 > There is a problem for this program, can you find out?
 
+#### Critical Situations
+
+- **Memory leak**: if you forget to deallocate memory - your program **will eventually run out of memory**
+- **Double free**: if you call `free` twice on the same memory - possible **crash or exploitable vulnerability**
+- **Use after free**: if you use data after calling `free` - possible **crash or exploitable vulnerability**
+
+In short, too many bad things can happen if you don't manage the memory correctly!
+
+Any solution? Yes, use [valgrind](https://valgrind.org/).
 
 ## C Compilation Process