Help with C++ Program

**Bnchs** · 09-09-2006

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.

Code:

#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;
}

**bumfluff** · 09-09-2006

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.

**Cat** · 09-09-2006

Code:

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.

Code:

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.

**dwks** · 09-09-2006

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

Code:

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.

Code:

    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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