Thread: Help with C++ Program

  1. #1
    Registered User
    Join Date
    Sep 2006

    Help with C++ Program

    I am trying to write a program that will receive as input an item type and then depending on the input, calculate tax for it, etc. If the user does not enter a valid item type, it is supposed to ask the user to re-enter the correct item type. I am having problems with the condition section of the while loop. Can anyone suggest a hint to help me correct the problem? Thanks.

    #include <iostream>
    #include <string>
    #include <cstdlib>
    using namespace std;
    int main()
        double price ;
        double discount ;
        double tax ;
        double total ;
        double discount_amount ;
        double tax_amount ; 
        char item_type [8] ;
        cout << "Enter the Item Type: food, clothes, toys, or other: " ; 
        cin >> item_type ;
        while (item_type == "food" || item_type == "clothes" || item_type == "toys"
        || item_type == "other")
        cout << "Enter Item Price : $" ;
        cin >> price ; 
        cout << "Enter Discount Percentage (%): " ;
        cin >> discount ;
        // Checks if item is taxable and calculates tax.
        if (item_type == "toys" || item_type == "other")
                    {   cout << "Enter Tax Percentage (%): " ;
                        cin >> tax ;
                    }   cout << endl ;
        cout << "The Item Price is: $" << price << "." <<endl ;
        discount_amount = price - (price * (discount/100));
        cout << "The Discount Amount is: $" << discount_amount << endl ;
        tax_amount = (price - (price * (discount/100))) * (tax/100);
        cout << "The Tax Amount is : $" << tax_amount << endl ;
        cout << "The Final Bill Amount is : $" << discount_amount + tax_amount ; 
        cout << endl ;   
        cout << "Please Enter a Valid Item Type: " <<endl ;
        cin >> item_type ;
        system("PAUSE") ;
        return 0;

  2. #2
    Registered User
    Join Date
    Nov 2005
    It looks to me as though you have it the wrong way round, you should just have a do...while loop for the input, so it does it while the input is incorrect and then it continues to do all the calculations.

  3. #3
    Registered User
    Join Date
    May 2003
    char item_type [8] ;
    cin >> item_type ;
    Very bad idea. As soon as the user types 8 characters (because they will become 9 with a trailing \0), you have a buffer overrun.

    In general, you should NEVER fill a char[] buffer except if the function has an argument to specify the maximum number of characters it's allowed to read.

    Fix this by using a std::string for the item_type. The string will adjust its size to be large enough to store the input.

    That also will solve another major problem, which is you can't use == with C-style strings.

    char item_type[8];
    if (item_type == "toys")
    That if statement will ALWAYS return false, because it's comparing them as pointers. That is, the if statement is actually asking "Is the memory address where item_type is stored the same as the memory address where the constant string literal "toys" is stored?"

    And that will always, always be false. There is a way to fix that (using C-style string compares) but that's the bad fix. The best fix is a std::string, where == does what you think it does, string comparison.
    Last edited by Cat; 09-09-2006 at 06:42 PM.
    You ever try a pink golf ball, Wally? Why, the wind shear on a pink ball alone can take the head clean off a 90 pound midget at 300 yards.

  4. #4
    Frequently Quite Prolix dwks's Avatar
    Join Date
    Apr 2005
    You don't need to put a space before each semicolon (although there's no harm in doing so).

    You have a problem with your code; an uninitialized variable. What if this if
    if (item_type == "toys" || item_type == "other")
    is false? tax won't be set to anything, but you use tax anyway. tax will be a random value (say 2.7847959e-55), and your calculations will be . . . off.

        cout << "Please Enter a Valid Item Type: " <<endl ;
        cin >> item_type ;
        system("PAUSE") ;
        return 0;
    I think you need a loop here, because as written, that will prompt you for something and do nothing with the value.

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