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

您对A，B或C的测试是错误的

 while (package != 'A' || package != 'B' || package != 'C')

应该是

 while (package != 'A' && package != 'B' && package != 'C')

Answer 2

考虑你的表达：

while (package != 'A' || package != 'B' || package != 'C') {

让包的值为'A'。

评估为

false || true || true

这当然是真的。

Answer 3

此行始终评估为true：

while (package != 'A' || package != 'B' || package != 'C')

应该是：

while (package != 'A' && package != 'B' && package != 'C')

Answer 4

您应该检查cin是否能够流式传输所需类型的值ala if (cin >> my_int)，然后在错误输入后使用std::cin.clear()，然后再重新输入值。否则，垃圾值，例如说某些无法转换为int的文本输入会使std::cin处于错误状态，并且甚至不会尝试下一个std::cin >> xxx。

Answer 5

“while”只会在您需要时循环播放，但“if”将始终触发;你是这个意思吗？关于A，B或C的“if”总是触发，因为你使用了“||”意思是“或”链接条件。对于你的变量的任何值，它总是正确的，它不是A，不是B，或者不是C！

Answer 6

首先，这段代码：

//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;
}

不起作用，因为（1）你将字符串（包）与字符进行比较，（2）你正在使用|| （或）代替＆amp;＆amp; （和）。另外（3）你可能想要“while”而不是“if”。

while循环对我来说很好。

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;
}

如果在循环内输入package值为 B ，该怎么办？它满足第一个条件package != 'A'，因为它之后是 OR 操作（ true || false || true 导致 true ），循环进入。您应该使用&&代替。所以，改变

 while (package != 'A' && package != 'B' && package != 'C')
 {
     // .....
 }

为什么我的“while”循环无论我输入什么都会执行？

7 个答案: