Pass by value, pass by reference, pass by pointers.

	#include<iostream>
	void change_var(int &a) //here a is an reference to variable 'x'
	{
	a++;
	}

	int main()
	{
	int x=20;
	std::cout<<x<<std::endl; //will print 20
	change_var(x);
	std::cout<<x<<std::endl;  //will print 21
	return 0;
	}

• Pass by pointers will also change the data globally. It is suggested to use pass by reference over pointers.
• have a look at the code:

  	#include<iostream>
  	int * change_var(int *a) //here a is an pointer to variable 'x' and a stores memory address of varialbe x. 
  	{
  		(*a)++; //we need to dereference the pointer to access its value. 'a' holds the address and *a has its value. note that *a++ won't work and it will increase the value of address by one. 
  		*a++; //trying to increase value of a, but in fact it increases pointer value. It is same as saying a++.
  		return a;
  	}
  	int main()
  	{
  	int x=20;
  	std::cout<<"address of x is "<<&x<<std::endl;
  	int *a=change_var(&x);
  	std::cout<<x<<std::endl; //here value 20 is in x, and x is referenced by parameter/alias 'a'. the changes will be made in parameter 'a' and in variable 'x', it will generate output as : 21
  	std::cout<<"address after calling function is "<<a;
  	}
  

Output
address of x is 0x7ffcd5f30234
21
address after calling function is 0x7ffcd5f30238

Note that the address increase by 4, since now pointer points to next memory which is 4 blocks away (integer takes 4 bytes).