C++检查cin是否有有效数据不工作

Question

我正在为学校做一项作业，我正在使用一个包含国际民航组织字母表的数组。用户输入一个字母，然后该程序显示出国际民航组织的单词与所提供的信件的内容。我使用一个索引变量从民航组织数组中获取民航组织的单词。但是，我需要检查用户只输入一个字母才能进入char输入变量。我该怎么做？下面是我所拥有的，但没有正确地工作。它读取第一个字母，并从第一个字母中吐出结果，然后立即关闭。

int main()
string icao[26] = 
"Alpha",
 "Bravo",
 "Charlie",
 "Delta",
 "Echo",
 "Foxtrot",
 "Golf",
 "Hotel",
 "India",
 "Juliet",
 "Kilo",
 "Lima",
 "Mike",
 "November",
 "Oscar",
 "Papa",
 "Quebec",
 "Romeo",
 "Sierra",
 "Tango",
 "Uniform",
 "Victor",
 "Whiskey",
 "X-ray",
 "Yankee",
 "Zulu"
};
int index;
char i;
cout << "Enter a letter from A-Z to get the ICAO word for that letter: ";
while(!(cin >> i))
{
    cout << "Please enter a single letter from A-Z: ";
    cin.clear();
    cin.ignore(1000,'\n');
}
i = toupper(i);
index = int(i)-65;
cout << "The ICAO word for " << i << " is " << icao[index] << ".\n";

cin.get();
cin.get();
return 0;

}

，我从每个答案中找出了一些答案。解决方案如下：

int main()

//store all the ICAO words in an array
string icao[26] = 
{"Alpha",
 "Bravo",
 "Charlie",
 "Delta",
 "Echo",
 "Foxtrot",
 "Golf",
 "Hotel",
 "India",
 "Juliet",
 "Kilo",
 "Lima",
 "Mike",
 "November",
 "Oscar",
 "Papa",
 "Quebec",
 "Romeo",
 "Sierra",
 "Tango",
 "Uniform",
 "Victor",
 "Whiskey",
 "X-ray",
 "Yankee",
 "Zulu"
};
int index;
string input = "";
cout << "Enter a letter from A-Z to get the ICAO word for that letter: ";

// get the input from the user
cin >> input;
//get the first character the user entered in case the user entered more than one character
char input1 = input.at(0);
//if the first character is not a letter, tell the user to enter a letter
while (!isalpha(input1))
{
    cout << "Please enter a letter from A-Z: ";
    cin >> input;
    input1 = input.at(0);
    cin.clear();
}
//capitalize the input to match the internal integer for the characters
input1 = toupper(input1);
index = int(input1)-65;
cout << "The ICAO word for " << input1 << " is " << icao[index] << ".\n";

cin.get();
cin.get();
return 0;

Answer 1

你的支票

while( !cin ) 

检查流是否失败。或者其他原因。你想要完成的事情更棘手。也许您可以做一个getline( cin，string )来检查用户是否只输入一个字符，然后点击返回。

string input;
getline( cin, input );
if ( input.size() == 1 && *input.c_str()>='A' && *input.c_str()<='Z' )

或者其他类似的东西。请注意，这个条件与我认为您的with语句的意图正好相反。

Answer 2

好的。

所以std:cin是缓冲的，所以你可能需要输入"a“才能让它正常工作。

这对我来说很管用：

cin >> i:  reads the 'a' character.  
cin.get(): reads the enter character.
cin.get(): Waits for me to hit enter a second time before quitting.

注意:如果我输入"1“，它可以工作，但当我试图访问数组时会出现分段错误。