The default tool that Valgrind uses is Memcheck.  The Memcheck tool can detect quite an exhaustive list of issues, and some of them are as follows:

• Accessing outside the boundary of array, stack, or heap overruns
• Use of uninitialized memory
• Accessing the already released memory 
• Memory leaks
• Mismatched use of new and free or malloc and delete

Let's have a look at some such issues in the next subsections.