虽然声明不起作用?
问题描述:
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
int number;
float cost;
char beverage;
bool validBeverage;
cout << fixed << showpoint << setprecision(2);
do
{
cout << endl << endl;
cout << "Hot Beverage Menu" << endl << endl;
cout << "A: Coffee $1.00" << endl;
cout << "B: Tea $ .75" << endl;
cout << "C: Hot Chocolate $1.25" << endl;
cout << "D: Cappuccino $2.50" << endl <<endl << endl;
cout << "Enter the beverage A,B,C, or D you desire" << endl;
cout << "Enter E to exit the program" << endl << endl;
cin>>beverage;
while(beverage!='A'||beverage!='B'||beverage!='C'||beverage!='D'||beverage!='E'||beverage!='a'||beverage!='b'||beverage!='c'||
beverage!='d'||beverage!='e')
{
cout<<"Your selection is invalid please re-enter ";
cin>>beverage;
}
switch(beverage)
{
case 'a': validBeverage = true;
case 'A': validBeverage = true;
case 'b': validBeverage = true;
case 'B': validBeverage = true;
case 'c': validBeverage = true;
case 'C': validBeverage = true;
case 'd': validBeverage = true;
case 'D': validBeverage = true;
break;
default: validBeverage = false;
}
if (validBeverage == true)
{
cout << "How many cups would you like?" << endl;
cin>>number;
}
// Fill in the code to begin a switch statement
switch(beverage)
{
case 'a': cost = number * 1.0;
case 'A': cost = number * 1.0;
cout << "The total cost is $ " << cost << endl;
break;
case 'b': cost = number * 0.75;
case 'B': cost = number * 0.75;
cout<< "The total cost is $ " << cost << endl;
break;
case 'c': cost = number * 1.25;
case 'C': cost = number * 1.25;
cout << "The total cost is $ " << cost << endl;
break;
case 'd': cost = number * 2.50;
case 'D': cost = number * 2.50;
cout << "The total cost is $ " << cost << endl;
case 'e': cout << " Please come again" << endl;
case 'E': cout << " Please come again" << endl;
break;
default:cout << " You have enter an invalid selection"<<endl;
cout << " Try again please" << endl;
}
}while(beverage!='e'||beverage!='E');
}
我试图运行这个程序,但它总是让我输入一个无效的选择。 我试图修改while循环,但它没有工作;它是while循环吗? 也不知道我是否在正确的时候写了while语句。虽然声明不起作用?
答
变化
while(beverage!='e'||beverage!='E'); // Condition becomes true always
到
while(beverage!='e'&& beverage!='E');
并且类似地更换所有||
通过&&
在第一while循环条件表达式
while(beverage!='A' && beverage!='B' &&beverage!='C'&& beverage!='D' && beverage!='E' && beverage!='a' && beverage!='b' && beverage!='c' &&
beverage!='d' && beverage!='e')
答
取这种情况作为一个例子,同样的问题也在其他人身上。
while (beverage!='e'||beverage!='E');
甲字符是不等于'e'
,或它等于'e'
,在这种情况下,它不等于'E'
,所以条件是总是如此。
你想要的是合乎逻辑的。
'||'是OR。当然,“饮料”会与“A”不同或与“B”或“......”不同。您想要的是&&' – Angew 2014-09-12 14:35:58
代码风格评论:您正在过度使用案例延期。就像如果你喝“e”一样,它会打印“请再来”两次。 – Almo 2014-09-12 14:35:59
@Almo而且,更糟糕的是,要进行两次乘法运算。 – Angew 2014-09-12 14:36:19