Introductory C++ program - c++

Question

I have tried tirelessly to get this right, but nothing seems to work. A lot of what I do brings me to an error 'Control may reach end of non-void function'.
Basically, we created a program to output gas usage statistics. What I am stuck on is:
"Gas will rise in price from the defined initial value to the defined final value over the course of 4 years, then remain fixed at that higher value for the next 4 years."
I feel like there should be a loop or function for this, but every time I make NUM_YEARS an int rather than a const, no matter what the program tells me 'Control may reach end of non-void function.'
Below is the program:
#include <cstdlib>
#include <iostream>
using namespace std;
const int MILES_PER_YEAR = 21000;
const double CITY_PERCENT = 45.0;
const double HIGHWAY_PERCENT = 55.0;
const double CITY_MPG = 51.0;
const double HIGHWAY_MPG = 45.0;
const double USABLE_GAS = 9.0;
const double INITIAL_PRICE = 3.359;
const double FINAL_PRICE = 6.00;
const int NUM_YEARS = 8; //This will be the total number of years
double gasPrice(int day);
int main(int argc, char * argv[]) {
cout << "Driving the Toyota Prius" << endl;
double daily_miles = MILES_PER_YEAR / 365.0;
double daily_city_miles = daily_miles * CITY_PERCENT/100.0;
double daily_highway_miles = daily_miles*HIGHWAY_PERCENT/100.0;
double daily_gas_consumed = daily_highway_miles / HIGHWAY_MPG +
daily_city_miles / CITY_MPG;
double gas_in_tank = USABLE_GAS;
double price;
double amount_purchased;
double gallons_purchased;
double total_gas_purchases = 0;
for(int day = 0;day < 365*8; day++) { //If the day is less than the total number of days in 8 years, add one day
cout << "Driving summary for day " << day << endl;
cout << " highway miles: " << daily_highway_miles << endl;
cout << " city miles : " << daily_city_miles << endl;
cout << " gas consumed : " << daily_gas_consumed << endl;
gas_in_tank = gas_in_tank - daily_gas_consumed;
cout << " gas in tank : " << gas_in_tank << endl;
if (gas_in_tank < 0.0) {
cout << " BUY GAS" << endl;
gallons_purchased = USABLE_GAS - gas_in_tank;
price = gasPrice(day);
cout << " price today is : " << price << endl;
cout << " Gallons purchased: " << gallons_purchased << endl;
cout << " fillup cost : " << gallons_purchased * price << endl;
total_gas_purchases = total_gas_purchases + gallons_purchased * price;
cout << " total gas cost : " << total_gas_purchases << endl;
gas_in_tank = USABLE_GAS;
}
}
system("PAUSE");
return EXIT_SUCCESS;
}
double gasPrice(int day, int YEAR_NUM) {
if (int day=365) { //call YEAR_NUM, for day=365, increase YEAR_NUM by 1
YEAR_NUM++;
day = 0;
}
if (YEAR_NUM >= 4) {
double currentPrice = FINAL_PRICE;
currentPrice;
}
if (YEAR_NUM < 4) { //conditional price for the first four years
double dailyIncrease = (FINAL_PRICE - INITIAL_PRICE) / (NUM_YEARS * 365);
double currentPrice = (INITIAL_PRICE + day * dailyIncrease);
return currentPrice;
}
}

Answer 1

You need to return something in gasPrice that is outside of the for loop. The compiler is saying there is a chance that neither of the while conditions will be met, in which case there is no value to return.
On another note, the while loops do not make a lot of sense the way they are written. Just make them if statements.

Answer 2

I think if you move "return currentPrice;" out of those two while loops, it will fix the problem.

Answer 3

Function gasPrice has no return statement outside the for loop. As the function has a return type that is not void then if the return statement is absent the behaviour of the function will be undefined.