Why does my "while" loop execute no matter what i enter? - c++

Question

/*********************************************************
** Purpose: Asks the user for cable package they bought **
** and the amount of hrs they used and //tells them **
** their monthly bill **
**********************************************************/
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
//Defining variables
double hours_over; //Amount of hrs the user went over their monthly allottment
double extra_pay; //Extra bill amount for going over monthly hrs allotted
double monthly_bill; //Monthly bill the user will pay
int hours; // How many hours the user used during the month
char package; //The package the user chose
//Getting the package the user bought
cout << "Your monthly subscription bill is based on your package.";
cout << "\n\nWhat package did you buy? Enter A, B or C: ";
cin >> package;
//Validating user input-must enter A, B or C
while (package != 'A' || package != 'B' || package != 'C')
{
cout << "\nPlease enter A, B or C(capitalized).";
cout << "\n\nWhat package did you buy?: ";
cin >> package;
}
//Getting hours the user used during month
cout << "How many hours did you use?: ";
cin >> hours;
//Validating user input-hrs cant exceed 744
while (hours > 744)
{
cout << "I'm sorry but your monthly usage cannot exceed 744 hrs.";
cout << "\nPlease enter another number.";
cout << "How many hours did you use?: ";
cin >> hours;
}
//Fixing decimal place of answers
cout << setprecision(2) << fixed << showpoint << endl;
//Switch statement-go to the package the user bought
switch (package)
{
case 'A':
if (hours > 10)
{
hours_over=hours-10;
extra_pay=hours_over*(2.00);
monthly_bill=9.95+extra_pay;
cout << "Your monthly bill is: $" << monthly_bill << endl;
}
else
{
cout << "Your monthly bill is: $9.95";
}
break;
case 'B':
if (hours > 20)
{
hours_over=hours-20;
extra_pay=hours_over;
monthly_bill=14.95+extra_pay;
cout << "Your monthly bill is: $" << monthly_bill << endl;
}
else
{
cout << "Your monthly bill is: $14.95";
}
break;
case 'C':
cout << "Your monthly bill is: $19.95";
break;
default:
break;
}
cin.get();
return 0;
}

Answer 1

Your test for A, B, or C is wrong
while (package != 'A' || package != 'B' || package != 'C')
should be
while (package != 'A' && package != 'B' && package != 'C')

Answer 2

Consider your expression:
while (package != 'A' || package != 'B' || package != 'C') {
Let package have the value 'A'.
This evaluates to
false || true || true
which is of course true.

Answer 3

This line always evaluates to true:
while (package != 'A' || package != 'B' || package != 'C')
it should probably be:
while (package != 'A' && package != 'B' && package != 'C')

Answer 4

You should be checking to see if cin has been able to stream a value of the desired type, ala if (cin >> my_int), then using std::cin.clear() after an erroneous input before getting them to reenter the value. Otherwise, garbage values like say some text input that can't be converted to an int leave std::cin in an error state and the next std::cin >> xxx isn't even attempted.

Answer 5

The "while" will only loop when you want it to, but the "if" will always fire; is that what you mean? The "if" concerning A, B, or C always fires because you've used "||" meaning "or" to link conditions. It is always true, for any value of your variable, that it's not A, or not B, or not C!

Answer 6

First of all, this code:
//Validating user input-must enter A, B or C
if (package != 'A' || package != 'B' || package != 'C')
{
cout << "\nPlease enter A, B or C(capitalized).";
cout << "\n\nWhat package did you buy?: ";
cin >> package;
}
won't work, because (1) you're comparing a string (package) to characters, and (2) you're using || (or) instead of && (and). Also (3) you probably want "while" instead of "if".
The while loop worked fine for me.

Answer 7

cin >> package;
//Validating user input-must enter A, B or C
while (package != 'A' || package != 'B' || package != 'C')
{
cout << "\nPlease enter A, B or C(capitalized).";
cout << "\n\nWhat package did you buy?: ";
cin >> package;
}
What if the package value is B entered inside the loop. It satisfies the first condition package != 'A' and since it is an OR operation after it( true || false || true leads to true), loop enters. You should use && instead. So, change
while (package != 'A' && package != 'B' && package != 'C')
{
// .....
}