递归函数 - 输出不正确

Question

I am creating a program that uses recursion functions to count the vowels in a sentence and to determine if it is a palindrome. The problem I am getting is that it says the sentence entered is not palindrome even if it is.. Any help with this will be greatly appreciated. Thank you.

#include<iostream> 
#include <cmath>


using namespace std;

struct Sentence
{
    int CountVowels(string , int);

    public:
    Sentence (string);
    bool isPal(string , int);
    void Print();
    string s;
    int numVowel;
    int length;
    //~Sentence();

};

Sentence :: Sentence (string b)
{
    s = b;
    length = 0;
    numVowel = CountVowels(s, 0);
}

int Sentence :: CountVowels(string myWord, int startindex)
{
    length ++;
    int pandi; 

    if(myWord[startindex])
    {
        if (myWord[startindex] != 'a' && myWord[startindex] != 'e' && myWord[startindex] != 'i' && myWord[startindex] != 'o' && myWord[startindex] != 'u')
        {
            pandi = 0;
        }
    else pandi = 1;
    return pandi + CountVowels(myWord, startindex + 1);
    } 
    return 0;
}

bool Sentence :: isPal(string myWord, int size)
{
    int r = myWord.size() - size;
    int t = size - 1;


    if (size == r || r == t)

        return true;


    if ((myWord[r]) != (myWord[t]))

        return false;


    return isPal(myWord, -- size);
}

void Sentence :: Print()
{
    cout << s [-- length];
    if (length == 0)
    {
        cout << endl;
        return;

    }
    Print ();
}

/*Sentence :: ~Sentence()
{
    cout << "\ntilde delete\n\n";
}*/

int main ()
{
    string userW;

    cout << "Enter a sentence: \n";
    getline(cin, userW);
    userW.erase(remove_if(userW.begin(), userW.end(), [](char c) {return !isalpha(c); }), userW.end());
    Sentence userSent(userW);

    cout << "The number of vowels in the sentence is " << userSent.numVowel << endl;
    cout << "" << endl;

    cout << "The sentence " << userSent.s << " is" << 
    (userSent.isPal(userSent.s, userSent.s.size()) ? " Palindrome\n" : " Not Palindrome\n");


    return 0;
}

UPDATE: I am now trying to remove special characters. So it looks like this

string userW;

        cout << "Enter a sentence: \n";
        getline(cin, userW);
        userW.erase(remove_if(userW.begin(), userW.end(), [](char c) {return !isalpha(c); }), userW.end());

But I am getting this error:

In function 'int main()':
88:85: error: 'remove_if' was not declared in this scope

Answer 1

Your code is fine except that it does not remove commas, spaces and anything that is not alphabetic from the sentence. Also, you need to do a case-insensitive comparison on the characters. This is required, otherwise the examples

A man, a plan, a canal, Panama

Desserts, I stressed

would not be palidromes.

To remove special characters from the user input, you can use lambda

string userW; cout << "Enter a sentence: \n"; getline(cin, userW);
userW.erase(remove_if(userW.begin(), userW.end(), [](char c) {return !isalpha(c); }), userW.end());

EDIT you can also try the following to avoid the need for lambda:

  userW.erase(std::copy_if(userW.begin(), userW.end(), userW.begin(), isalpha), userW.end());

to do a case-insensitive comparison, in the function isPal, you can change this:

if ((myWord[r]) != (myWord[t]))

into this:

if (tolower(myWord[r]) != tolower(myWord[t]))

Answer 2

I have reviewed your program. You are trying to out the string in the function pirnt(). Here is the problem ,when you use

 cout << "The sentence backwards is: " << userSent.Print();

but funtion Print() does not have any return type.(because this is void type). Here you should use

cout << "The sentence backwards is: " ;
 userSent.Print();

and now it works.