what does realloc do in c code example

Example 1: realloc in c

void *realloc(void *ptr, size_t size)

Example 2: realloc

int ptr_new = *realloc(void *ptr, size_t size); 
Where 'ptr_new' is the new pointer you want to point to the required Dynamic
memory, 'ptr' is the already existing pointer to a dynamic memory and 'size'
is the new size of dynamic memory that you want to allocate.

Working:
Realloc creates/allocates a new memory in heap with specified size and copies
all the contents from the previous memory pointer to by the pointer 'ptr'.
It the deallocates the memory in heap pointed to by the old pointer i.e, 'ptr'.
Note: pointer 'ptr' should also point to a memory in heap.