Question

当我在C ++中使用以下代码时，我得到一个无限循环，我不明白为什么。我怀疑问题是在input_words()函数内。这是代码：

#include<iostream>
using namespace std;

string input_words(int maxWords) {
    int nWord = 0;
    string words[maxWords];
    string aWord = "";
    while (aWord != "Quit" && nWord < maxWords) {
        cout << "Enter a number ('Quit' to stop): ";
        getline (cin, aWord);
        words[nWord] = aWord;
        nWord++;
    }
    return *words;
}

int num_words (string words[], int maxWords) {
    int numWords = 0;
    for (int i=0; i<maxWords; i++) {
        if (words[i] == "Quit") {
            break;
        }
        numWords++;
    }
    return numWords;
}

int main() {

    const int MAX_WORDS = 100;
    string words[MAX_WORDS] = input_words(MAX_WORDS);

    int lenWords = num_words(words, MAX_WORDS);
    cout << "\nThere are " << lenWords << " words:\n";

    for (int i=0; i<MAX_WORDS; i++) {
        if (words[i] == "Quit") {
            break;
        }
        cout << words[i] << "\n";
    }
    return 0;
}

更具体地说，即使在提示输入单词时输入“退出”，我也无法退出。我该怎么解决这个问题？我知道这是noob代码:)我刚刚开始使用C ++

Answer 1

我以这种方式修改了这个功能：

string input_words(int maxWords) {
    cout << "started" << endl;
    int nWord = 0;
    string words[maxWords];
    string aWord = "";
    while (aWord != "Quit" && nWord < maxWords) {
        cout << "Enter a number ('Quit' to stop): ";
        getline (cin, aWord);
        words[nWord] = aWord;
        nWord++;
    }
    cout << "finished" << endl;
    return *words;
}

输入Quit后，打印“已完成”，然后再次“启动”。您的代码多次调用该函数。

问题是该函数只返回一个字符串。所以这一行

string words[MAX_WORDS] = input_words(MAX_WORDS);

似乎调用函数input_words MAX_WORDS次。

一种好方法是切换到vector<string>：

vector<string> input_words(int maxWords) {
    vector<string> words;
    string aWord;
    while (aWord != "Quit" && nWord < maxWords) {
        cout << "Enter a number ('Quit' to stop): ";
        getline (cin, aWord);
        words.push_back(aWord);
    }
    return words;
}

...
vector<string> words = input_words(MAX_WORDS);

Answer 2

我尝试了以下测试程序，它可以工作：

{0,506}$> cat testcin.cpp && make testcin && ./testcin.exe
#include <iostream>
using namespace std;

int main()
{
    const int maxWords = 5;
    int nWord = 0;
    string words[maxWords];
    string aWord = "";
    while (aWord != "Quit" && nWord < maxWords) {
        cout << "Enter a number ('Quit' to stop): ";
        getline (cin, aWord);
        words[nWord] = aWord;
        nWord++;
    }    
}

make: `testcin' is up to date.
Enter a number ('Quit' to stop): test
Enter a number ('Quit' to stop): Quit

[Vlad@rabbit] [20:53:53] [~/c++]
{0,507}$>

Answer 3

问题，我认为在您的主要位置返回input_words() string的结果，main()初始化字 string[]输入vector。这绝对是个问题。

重写为使用#include<iostream> #include<vector> #include<string> using namespace std; vector<string> input_words(int maxWords) { int nWord = 0; vector<string> words; string aWord = ""; while (aWord != "Quit" && nWord < maxWords) { cout << "Enter a number ('Quit' to stop): "; getline (cin, aWord); words.push_back(aWord); nWord++; } return words; } int num_words (vector<string> words) { // return words.size(); int numWords = 0; vector<string>::iterator it = words.begin(); for (; it != words.end(); it++) { if (*it == "Quit") { break; } numWords++; } return numWords; } int main() { const int MAX_WORDS = 100; vector<string> words = input_words(MAX_WORDS); int lenWords = num_words(words); cout << "\nThere are " << lenWords << " words:\n"; vector<string>::iterator it = words.begin(); for (; it != words.end(); it++) { if (*it == "Quit") { break; } cout << *it << endl; } return 0; }：

getline()

忘记以下内容，C ++ getline()会自动删除'\ n'。

您是否检查过"Quit" != "Quit\n".字是否在其末尾有换行符？也就是说，

{{1}}

C ++不需要的无限循环

3 个答案: