#include <iostream>
using namespace std;

int myFun( int a ); // function "prototype"
void myFun2( int a );
void myFun3( int &a );

// main function
int main() {
  int mynumber, n7;  
  cout << "hello user! please enter a number: "; // prompt user for input
  cin >> mynumber; // read user's number
  cout << "you entered: " << mynumber << endl; // echo back user's input
  // call the function myFun to multiply user's number by 7
  n7 = myFun( mynumber );
  cout << "your number times 7 = " << n7 << endl;
  // now call myFun2 to change the value of 'mynumber' (but it won't work)
  myFun2( mynumber );
  cout << "mynumber is now: " << mynumber << endl;
  // now call myFun3 to change the value of 'mynumber' (which will work)
  myFun3( mynumber );
  cout << "mynumber is now: " << mynumber << endl;
} // end of main()

// define function
int myFun( int a ) { // a is the function argument or parameter
  int b; // b is a local variable
  b = a * 7;
  return( b ); // return value
} // end of myFun()

void myFun2( int a ) { // this won't work because the value of a will
  a = a * 7;           // not be changed outside of the function
  cout << "inside myFun2: a=" << a << endl;
  return;
} 

void myFun3( int &a ) { // this will work because a is a reference parameter
  a = a * 7;           // and WILL be changed outside of the function
  cout << "inside myFun3: a=" << a << endl;
  return;
}