What is a memory leak and how can it be avoided?

Memory leak is a condition when a programmer who creates a memory in the heap forgets to delete it. It can be avoided by using the following coding:

/* Function without memory leak */
#include < stdlib.h > 
  
void f() 
{ 
   int *ptr = (int *) malloc(sizeof(int));  
   /* Do some work */  
   free(ptr); 
   return; 
}