Thread: arity

If the arity of the “+” operator is 2, why is there only one formal parameter in operator+’s function header?

Code:

#include <iostream>
#include <string>

using namespace std;

const int SIZE = 10;

class Bank_Acct
{
public:
	Bank_Acct( );  // default constructor
	Bank_Acct(double new_balance, string Cname); // explicit value 										    
	                                             // constructor
	void Print( ); //accessor function
	Bank_Acct & operator+(double amount); // mutator function

private:
	double balance;
	string name;
};

Bank_Acct::Bank_Acct()
{
	balance = 0;
	name = "NoName";
}

Bank_Acct::Bank_Acct(double amount, string Cname)
{
	balance = amount;
	name = Cname;
	
}

void Bank_Acct::Print()
{
	cout << endl << "Object name: " << name;
	cout << endl << "The new balance is: " << balance << endl;
}

Bank_Acct & Bank_Acct::operator+(double amount)
{
	balance += amount;
	return *this;
}

int main()
{
	Bank_Acct my_Acct;

	cout.setf(ios::showpoint);
	cout.setf(ios::fixed);
	cout.precision(2);

	cout << "Original balance of my_Acct:" << endl;
	cout << "----------------------------" << endl;
	my_Acct.Print( );

	// the following statement contains chaining
	my_Acct + 18.75 + 14.35 + 10054.96;

	cout << endl << endl;

	cout << "The balance of my_Acct after addition to balance 3 times:" << endl;
	cout << "---------------------------------------------------------" << endl;
	my_Acct.Print();

	cout << endl << endl;

	return 0;
}