Variables, Stack, Heap and default values in C#

Stack and Heap

Stack:

• It is a block of memory which stores local variables and parameters.
• The important logic of the stack is that it grows with the entry of the function and shrinks again when it is exited.
• Let's take an example code,
  

  using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Threading.Tasks;
  
  namespace Man
  {
      class Program
      {
          static int Main(int a)
          {
              if (a == 0)
                  return 1;
              return a + Main(a + 1);
          }
      }
  }

  The above method is the recursive method, which means the method calling itself. So, for every entry of the method, a new int is allocated on the stack and deallocated after its exit.

Heap:

• Heap is a block of memory which is derived to store objects (means reference type instances).
• When a new object is created in a method, it is stored (allocated) on the heap and returns a reference to that object.
• Objects created are gets filled on the heap during the execution of the program.
• Runtime contains a Garbage Collector which deallocates (removes) the objects simultaneously. Hence, the memory is cleared, which means our computer does not run out of the memory.
• Lets take an example code.
  

  using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Threading.Tasks;
  
  namespace Man
  {
      class Program
      {
          static void Main()
          {
              StringBuilder strb1 = new StringBuilder("Obj1");
  
              Console.WriteLine(strb1);  // Prints Obj1
  
              StringBuilder strb2 = new StringBuilder("Obj2");
              StringBuilder strb3 = strb2;
  
              Console.WriteLine(strb3);  // Prints Obj2
          }
      }
  }
  

  In the above code, we have created three StringBuilder objects srtb1, strb2 and strb3.
• First StringBuilder object "Obj1" is referenced by strb1 which has immediate eligible for Garbage Collection, because no other method or object is using it.
• And we also have strb2 which is accessed by strb3. Hence it doesn't become eligible for collection until we finish the usage of strb3.
  
• The output of the above code will be,
  
  
• Value type instances are active at the place where variable was declared.
• If any instance that declared as a field of an object (or an array element), that instance lives (remains active) on the heap.
• Heap also has the ability to store constants and static fields.

Definite Assignment

Default Values

• For all reference types - null
• For all numeric and enum types - 0
• For bool type - false
• For char type - '\0'

Conclusion