Non-lvalue in Program Question

Hello,
The errors are at the bottom of the post, and they are about the error: non-lvalue.
I am writing a program which allows the user to choose a beverage, sandwich and side order from a menu. After the choices are made, the program should do the following:

* list the items chosen with the cost of each item
* the sub-total of just the items
* the total cost including tax (use 6.5% for the tax).

The following are the items and prices I will include:

Beverages:
1: Soda: $0.99
2: Milk: $0.79
3: Juice: $1.29

Sandwiches:
1: Hamburger: $0.99
2: Cheeseburger: $1.09
3: Chicken Sandwich: $2.59

Side Orders:
1: French Fries: $0.89
2: Onion Rings: $1.09
3: Corn Chips: $0.59

The output should look something like this (it must include the items and prices, the sub-total, the tax, and the total cost including tax)

Soda: $0.99
Hamburger: $0.99
French Fries: $0.89

Total of food: $2.87
Tax: $0.19
Total for order: $3.06

Code:

#include <iostream>
#include <string>
int main ()
{
int drink;
int sandwich;
int side;
double price;
double soda;
double milk;
double juice;
double hamburger;
double cheeseburger;
double chicken;
double fries;
double rings;
double chips;
soda = .99;
milk = .79;
juice = 1.29;
hamburger = .99;
cheeseburger = 1.09;
chicken = 2.59;
fries = .89;
rings = 1.09;
chips = .59;
cout << "Pick Drink & input coresponding number" << endl;
cout << "1: Soda $0.99" << endl;
cout << "2: Milk $0.79" << endl;
cout << "3: Juice $1.29" << endl;
cin >> drink;
	if (drink == 1)
	{price + soda = price;}
	if (drink == 2)
	{price + milk = price;}
	if (drink == 3)
	{price + juice = price;}

cout << "Pick Sandwich & input coresponding number" << endl;
cout << "1: hamburger $0.99" << endl;
cout << "2: cheeseburger $1.09" << endl;
cout << "3: chicken $2.59" << endl;
cin >> sandwich;
	if (sandwich == 1)
	{price + hamburger = price;}
	if (sandwich == 2)
	{price + cheeseburger = price;}
	if (sandwich == 3)
	{price + chicken = price;}

cout << "Pick Side & input coresponding number" << endl;
cout << "1: fries $0.89" << endl;
cout << "2: onion rings $1.09" << endl;
cout << "3: corn chips $0.59" << endl;
cin >> side;
	if (side == 1)
	{price + fries = price;}
	if (side == 2)
	{price + rings = price;}
	if (side == 3)
	{price + chips = price;}

if (drink == 1)
cout << "Soda: $0.99" << endl;
if (drink == 2)
cout << "Milk: $0.79" << endl;
if (drink == 3)
cout << "Juice: $1.29" << endl;

if (sandwich == 1)
cout << "Hamburger: $0.99" << endl;
if (sandwich == 2)
cout << "Cheeseburger: $1.09" << endl;
if (sandwich == 3)
cout << "Chicken: $2.59" << endl;

if (side == 1)
cout << "Fries: $0.89" << endl;
if (drink == 2)
cout << "Onion Rings: $1.09" << endl;
if (drink == 3)
cout << "Chips: $0.59" << endl;


cout << "Price: " << price << endl;
cout << "Tax: " << price * .065 << endl;
cout << "Total: " << price * 1.065 << endl;

return 0;
}

That is what I have.
Here are the errors that display:

Code:

menu.cpp: In function `int main()':
menu.cpp:33: non-lvalue in assignment
menu.cpp:35: non-lvalue in assignment
menu.cpp:37: non-lvalue in assignment
menu.cpp:45: non-lvalue in assignment
menu.cpp:47: non-lvalue in assignment
menu.cpp:49: non-lvalue in assignment
menu.cpp:57: non-lvalue in assignment
menu.cpp:59: non-lvalue in assignment
menu.cpp:61: non-lvalue in assignment

I do not know what non-lvalue means, so it would be great if someone could help me out there, it would be greatly appreciated!
Thank you!

This (and all like it) is backwards:

Code:

price + soda = price;

Should be

Code:

price = price + soda;

or

Code:

price += soda;

An l-value (left value) is something that can be assigned to.

Yes!
I remember that now.
Now it is working!
Thank you nucleon!