Non-lvalue in Program Question

This is a discussion on Non-lvalue in Program Question within the C++ Programming forums, part of the General Programming Boards category; Hello, The errors are at the bottom of the post, and they are about the error: non-lvalue. I am writing ...

  1. #1
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    Nov 2008
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    21

    Question 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!

  2. #2
    Registered User
    Join Date
    Oct 2008
    Posts
    55
    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.

  3. #3
    Registered User
    Join Date
    Nov 2008
    Posts
    21
    Yes!
    I remember that now.
    Now it is working!
    Thank you nucleon!

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