#include <iostream>

using namespace std;

float sum (float &int1, float &int2);   //function prototype sum
float minus (float &int1, float &int2);   //function prototype minus
float mult (float &int1, float &int2);   //function prototype mult
float divide (float &int1, float &int2);   //function prototype divide

int main()  //function main
{
	float a =0;
	float b =0;	
	int choice =0;
	
	cout.setf(ios::showpoint);  //always show decimal
	cout.setf(ios::fixed);
	cout.precision(2);		//set output to two digits
	
	do {
	cout << "Welcome to the calculator please make a choice:""\n\n";
	cout << "(1) Add two numbers.""\n";
	cout << "(2) Subtract two numbers.""\n";
	cout << "(3) Mutiply two numbers.""\n";
	cout << "(4) Divide two numbers.""\n";
	cout << "(5) Exit.""\n\n";
	cin  >> choice;
	
	
	switch (choice)
	{
	case 1:
			cout << "Enter numbers to add.  ";
			cin >> a >> b;
			cout << "The product of your two numbers is "<< sum(a,b) <<"\n";
			break;
	case 2:
			cout << "Enter numbers to subtract.  ";
			cin >> a >> b;
			cout << "The subtraction of your two numbers is "<< minus(a,b) <<"\n";
			break;
	case 3:
			cout << "Enter numbers to multiply.  ";
			cin >> a >> b;
			cout << "The multpication of your two numbers is "<< mult(a,b) <<"\n";
			break;
	case 4:
			cout << "Enter numbers to divide.  ";
			cin >> a >> b;
			cout << "The division of your two numbers is "<< divide(a,b) <<"\n";
			break;
	default:
		break;
	}

		}while (choice!=5);
	return 0;

} // end main

//---------------------------------------------------------------------------------------------------------
// Define the sum function.

float sum(float &x, float &y)		// This function returns the sum of its arguments.
{return (x + y);}
									
float minus(float &x, float &y)		// This function returns the subtraction of its arguments.
{return (x - y);}

float mult(float &x, float &y)		// This function returns the mutlipication of its arguments.
{return (x * y);}

float divide(float &x, float &y)		// This function returns the division of its arguments.
{return (x / y);}

void squareIt(int& value)
{
  value = value * value;
}

int main()
{
  int var = 3;
  squareIt(var);
  // var is now equal to 9.
}

int doubleIt(int value)
{
  value = value + value;
  return value;
}

int main()
{
  int var = 3;
  int result = doubleIt(var);
  // var is still 3.
  // result is equal to 6.
}

#include <iostream>
using std::cout;
using std::endl;

void byValue(int);//passing by value
void byRef(int &);//passing by ref

int main()
{
     int myVar = 100;
     cout << "now displaying the value of myVar passing by value:\n";
     byValue(myVar);
     cout << "\nnow displaying the value of myVar passing by reference:\n";   
     byRef(myVar);
     
     cout << endl;
     return 0;
}

//know we will display the value of the variable by value(a copy remember?)
void byValue(int localVar)
{
      //localVar is a copy of myVar
      cout << localVar;
}

//know displaying the value passed by reference
void byRef(int &localVar)//notice the "&" before localVar
{
      //here you r using the "original variable not a copy, so this function is best 
     //in performance 
      cout << localVar;
}