c++ - 当一切正确时，代码继续打印 "1"

Question

代码运行，但它没有打印出元音，而是打印出一个“1”。

#include <iostream>
#include <string>
using namespace std;

int countVowels(string sentence,int numVowels)
{
for(int i =0; i<sentence.length(); i++)
{
    if((sentence[i]==('a'))||(sentence[i]==('e'))||(sentence[i]==('i'))||(sentence[i]==('o'))||(sentence[i]==('u'))||(sentence[i]==('A'))||(sentence[i]==('E'))||(sentence[i]==('I'))||(sentence[i]==('O'))||(sentence[i]==('U')))
        numVowels=numVowels+1;

}

}

int main()
{
string sentence;
int numVowels = 0;
do{
cout << "Enter a sentence or q to quit: ";
cin >> ws;
getline(cin,sentence);
}
if(sentence == 'q'|| sentence == 'Q');



cout << "There are " << countVowels << " vowels in your sentence." << endl;

return 0;

}

输出应该是这样的:

输入一句话或a退出:我喜欢苹果!

你的句子中有 4 个元音字母和 11 个字母。

输入一句话或q退出:q

再见!

我的问题:有人可以向我解释为什么它一直打印“1”，而我应该分配热键“q”以退出程序的“if”语句不起作用。当我运行该程序时，我在 if 语句中收到错误消息“不匹配运算符==”

Answer 1

我通常不喜欢只提供一个完整的解决方案，但由于您的问题表明您已经做出了很好的努力，所以我会这样写(好吧，不完全是，我简化了一点以便对初学者更友好):

#include <algorithm>
#include <iostream>
#include <string>

bool isVowel(char c)
{
    // A simple function that returns true if the character passed in matches
    // any of the list of vowels, and returns false on any other input.
    if ( 'a' == c ||
         'e' == c ||
         'i' == c ||
         'o' == c ||
         'u' == c ||
         'A' == c ||
         'E' == c ||
         'I' == c ||
         'O' == c ||
         'U' == c) {
        return true; // return true if it's a vowel
    }

    return false; // remember to return false if it isn't
}

std::size_t countVowels(std::string const& sentence)
{
    // Use the standard count_if algorithm to loop over the string and count
    // all characters that the predicate returns true for.
    // Note that we return the resulting total.
    return std::count_if(std::begin(sentence),
                         std::end  (sentence),
                         isVowel);
}

int main() {
    std::string sentence;
    std::cout << "Please enter a sentence, or q to quit: ";
    std::getline(std::cin, sentence);

    if ( "q" == sentence ||
         "Q" == sentence) {
        // Quit if the user entered a string containing just a single letter q.
        // Note we compare against a string literal, not a single character.
        return 0;
    }

    // Call the counting function and print the result.
    std::cout << "There are "
              << countVowels(sentence) // Call the function on the input.
              << " vowels in your sentence\n";
    return 0;
}

希望评论能说明一切。

现在您可能被告知您不能使用标准算法 (std::count_if)，因为部分练习似乎是要编写它。好吧，我会把它留给你。您当前的版本接近正确，但请记住返回结果。而且您实际上不需要传入 numVowels 计数，只需在函数中创建它，并记得返回它。