//Define constants
const int MAX=5;  // vending items
const int QUARTERS=40;
const int DIMEs=50;
....


//Prototypes
void displayMenu();
int getOption();
double vendOption(int opt, int& chipsOnHand, int &gumOnHand, int &CurlsOnHand);


//Main
int main() {
	int opt;
	int chipsOnHand=MAX, gumOnHand=MAX, CurlsOnHand=MAX;

	double cost=0, total=0;
	do {
		displayMenu();
		opt=getOption();
		if (opt !=7){
		  cost =vendOption(opt, chipsOnHand, gumOnHand, CurlsOnHand);
		  total += cost;
		}
	} while (opt!=7);
	cout << "You owe " << total;
	return 0;
}
void displayMenu()
{
  // cout the 6 options and 7 for exit
}
int getOption()
{

   //get the option from the user
   // while the option is out of range, re-enter
   // return the validated option

}
double vendOption(int opt, int &chipsOnHand, int &gumOnHand, int &CurlsOnHand)
{
	double cost;
	switch (opt){
	  case 1: if (chipsOnHand == 0){
		  	    cout <<"Out of Chips. Try another option";
		  	    cost = 0;
	          }
	  	  else {
		      chipsOnHand--;
	  	      cost = 1.0;
	  	  }
	  	  break;
	  case 2: 
          ...
	  case 3:
	  ...
	}
	return cost;
}