Question

我正在编写一个程序来检查用户输入的字符串是否是回文即使字符串是已知回文，我的程序也始终返回false。我认为我的问题出在PalindromeChecker函数上，因为这总是将main函数中的answer变量设置为false。但是我不确定为什么总是这样。

#include "stdafx.h"
#include <iostream>
#include <String>

using namespace std;

char ReadPalIn(string Pal, int len)//converts the string into a char array
{
    char PalIn[100];
    if (len > 100)
    {
        cout << "ERROR: Palindrome possibliity too big" << endl;
        system("Pause");
    }
    else
    {
        for (int i = 0; i < len; i++)
        {
            PalIn[i] = Pal[i];
        }
    }
    return *PalIn;
}

bool PalindromeChecker(char Pal[],int start, int end)//checks recursively if a string is a palidrome
{
    if (start == end)
    {
        return true; //since there is only one character
    }
    else if (Pal[start] != Pal[end])
    {
        //cout << "hi" << endl;
        return false;//since that will be the case that decides when something stops being a palidrome
    }
    else if (start < end + 1)
    {
        //cout << "hi" << endl;
        return PalindromeChecker(Pal, start++, end--);//since we checked both the first and last characters of the char array for palandrominess. <- word of the year?
    }
    else
    {
        return true;//base case is the string is a palindrome
    }
}

int main()//test if a word is a palidrome using the functions
{
    int lengthOfPal = 0;
    string PalInd = "abba";
    bool Answer = true;
    cout << "Hello what string would you like to check?" << endl;
    getline(cin, PalInd);
    lengthOfPal = PalInd.length();
    cout << "You input is: " << PalInd << endl;
    cout << "Its Length is: " << lengthOfPal << endl;
    system("Pause");
    char PalIn[100] = { ReadPalIn(PalInd, lengthOfPal) };

    Answer = PalindromeChecker(PalIn, 0, lengthOfPal);
    if (Answer == true)
    {
        cout << PalInd << ": is a palidrome" << endl;
        system("Pause");
    }
    else if(Answer == false)
    {
        //cout << "hi" << endl;
        cout << PalInd << ": is not a palidrome" << endl;
        system("Pause");
    }
    return 0;
}

Answer 1

您总是返回false，因为您没有在比较自己认为的内容。

在最初调用PalindromeChecker()时，您将lengthOfPal用作end参数。由于字符串是零索引的，因此您的初始调用应使用lengthOfPal - 1。

假设您的字符串是abba。 a字符位于[0]和[s.length() - 1]（索引[3]）处。

您将要遇到的另一个问题是在递归调用中传递start++和end--作为参数。这些是后递增和后递减运算符，这意味着它将把start和end的 current 值传递到递归调用中，然后 then < / em>调整其值。由于您已将函数设置为递归，因此每次都只会对start和end使用相同的值。可以使用预递增++start和预递减--end来避免此问题。

字符串检查始终返回错误的回文

1 个答案: