Difference between const reference and normal parameter

Question

void DoWork(int n);
void DoWork(const int &n);

What\'s the difference?

Answer 1

There are three methods you can pass values in the function

1. Pass by value

   void f(int n){
       n = n + 10;
   }
   
   int main(){
       int x = 3;
       f(x);
       cout << x << endl;
   }
   

   Output: 3. Disadvantage: When parameter x pass through f function then compiler creates a copy in memory in of x. So wastage of memory.

2. Pass by reference

   void f(int& n){
       n = n + 10;
   }
   
   int main(){
       int x = 3;
       f(x);
       cout << x << endl;
   }
   

   Output: 13. It eliminate pass by value disadvantage, but if programmer do not want to change the value then use constant reference

3. Constant reference

   void f(const int& n){
       n = n + 10; // Error: assignment of read-only reference  ‘n’
   }
   
   int main(){
       int x = 3;
       f(x);
       cout << x << endl;
   }
   

   Output: Throw error at n = n + 10 because when we pass const reference parameter argument then it is read-only parameter, you cannot change value of n.