Check out example codes for "delete memory c++". It will help you in understanding the concepts better.

Code Example 1

// Release block of memory 
// pointed by pointer-variable
delete[] pointer-variable;  

   // It will free the entire array
   // pointed by p.
   delete[] p;

Code Example 2

//placement new in c++
char *buf  = new char[sizeof(string)]; // pre-allocated buffer
string *p = new (buf) string("hi");    // placement new
string *q = new string("hi");          // ordinary heap allocation
/*Standard C++ also supports placement new operator, which constructs 
an object on a pre-allocated buffer. This is useful when building a 
memory pool, a garbage collector or simply when performance and exception 
safety are paramount (there's no danger of allocation failure since the memory
has already been allocated, and constructing an object on a pre-allocated
buffer takes less time):

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