Question

当我输入0到9之间的任何数字时，我希望我的代码打印“您的汽车停在A区”。它正在输入，但是程序终止而没有进入if条件（我认为）

{  
    int value=0;
    cout<<"Enter car serial number"<<endl;
    cin>>value;
    if(value >= 48 && value <= 57)
    {
        cout<<"your car is parked in section Z"<<endl;
    }
}

Answer 1

您混淆获取整数和获取字符

拥有

int value
...
cin >> value;

您读取了一个 int ，因此输入2将 value 设置为值2，而不是字符'2'的（ascii）代码，当然如果输入的是123 value 我设置为123等

当然可以

 if(value >= 48 && value <= 57)

不是正确的，除了您输入介于48和57之间的值

做

 char c;

 cin >> c;

如果您输入2 c ，那么该时间将设置为'2'，因此ascii为50

当我输入0到9之间的任何数字时，我希望我的代码打印“您的汽车停在A区”。

我想0表示A，1表示B等，而不是总是A

例如，您可以做：

{  
    int value=0;
    cout<<"Enter car serial number"<<endl;
    cin>>value;
    if(value >= 0 && value <= 9)
    {
        cout<<"your car is parked in section " << *("ABCDEFGHIJ" + value) << endl; // makes no assumption concerning the alpha codes
    }
}

但要检查输入是否为有效整数更好：

{  
    int value=0;
    cout<<"Enter car serial number"<<endl;
    if (!(cin>>value))
    {
       cerr << "invalid input" << endl;

       cin.clear(); // raz error

       string s;

       if (! (cin >> s)) // fluxh input
         ..EOF do what you want...
    }
    else if(value >= 0 && value <= 9)
    {
        cout<<"your car is parked in section " << *("ABCDEFGHIJ" + value) << endl; // makes no assumption concerning the alpha codes
    }
    else
        cerr << "invalid serial number" << endl
}

根据您的评论：

我希望我的代码打印“您的汽车在“ this”部分中，其中“ this”可以是A，B或C，具体取决于汽车的序列号。如果是1-10，则应在此部分中A.如果是11-20，则在B部分。

{  
    int value=0;
    cout<<"Enter car serial number"<<endl;
    if (!(cin>>value))
    {
       cerr << "invalid input" << endl;

       cin.clear(); // raz error

       string s;

       if (! (cin >> s)) // fluxh input
         ..EOF do what you want...
    }
    else if(value >= 1 && value <= 260)
    {
        cout<<"your car is parked in section " << *("ABCDEFGHIJKLMNOPQRSTUVWXYZ" + (value-1)/10) << endl; // makes no assumption concerning the alpha codes
    }
    else
        cerr << "invalid serial number" << endl
}

示例：

#include <iostream>

using namespace std;

int main()
{  
  for (;;) {
    int value=0;
    cout<<"Enter car serial number"<<endl;
    if (!(cin>>value))
    {
       cerr << "invalid input" << endl;

       cin.clear(); // raz error

       string s;

       if (! (cin >> s)) // fluxh input
         return -1; // ..EOF do what you want...
    }
    else if(value >= 1 && value <= 260)
    {
        cout<<"your car is parked in section " << *("ABCDEFGHIJKLMNOPQRSTUVWXYZ" + (value-1)/10) << endl; // makes no assumption concerning the alpha codes
        return 0;
    }
    else
        cerr << "invalid serial number" << endl;
  }
}

编译和执行：

pi@raspberrypi:/tmp $ g++ -pedantic -Wall -Wextra s.c
pi@raspberrypi:/tmp $ ./a.out
Enter car serial number
-12
invalid serial number
Enter car serial number
0
invalid serial number
Enter car serial number
a
invalid input
Enter car serial number
1
your car is parked in section A
Enter car serial number
10
your car is parked in section A
pi@raspberrypi:/tmp $ ./a.out
Enter car serial number
11
your car is parked in section B
pi@raspberrypi:/tmp $ ./a.out
Enter car serial number
54
your car is parked in section F
pi@raspberrypi:/tmp $ ./a.out
Enter car serial number
250
your car is parked in section Y
pi@raspberrypi:/tmp $ ./a.out
Enter car serial number
251
your car is parked in section Z
pi@raspberrypi:/tmp $ ./a.out
Enter car serial number
260
your car is parked in section Z

这不是我想要的

1 个答案: