Thread: Purpose of Private and Public Access Specifiers, OOP

I was just wondering in my program, what exactly is the purpose of declaring private data members? What exactly is the concept behind, private and public?

Code:

#include<iostream> 

using namespace std; 
  
class Encapsulation   /*class name is Encapsulation */
{ 
    private:         /*access specifer */


        int x;      /* x is integer variable that store integer value */
          
    public:          /*access specifer */
       
        void set(int a)     /*function that pass integer value a */
        { 
            x =a;          /* we are assigning content of a to x */
        } 
          
        int get()         /* function that resturn value of x */
        { 
            return x;    /*return result of x */
        } 
}; 
  
int main()     /* start program */
{ 
    Encapsulation obj;   //declare object of job */
      
    obj.set(5);          // call function to pass 5
      
    cout<<obj.get();     /* get output of function 
    return 0; 
}