Question

我正在编写代码以检查句子是否是回文。我觉得我的逻辑是正确的，但是用于检查字符串反向的if语句似乎不起作用。我已经在网上尝试了许多解决方案，但仍然一无所获。每个字符串都不是回文。我觉得错误在于（句子==反向）：

#include <iostream>
#include <string>
#include <vector>
#include <fstream>
#include <sstream>

using namespace std;

int main(int argc, char *argv[])  {

while (true) {
  string sentence;
  string reverse = "";

  cout << "Enter a sentence below to check (-1 to end):" << endl;
  getline(cin, sentence);

  if (sentence == "q") {
    break;
  }

  for (int i = sentence.length(); i >= 0; i-- ) {
    reverse += sentence[i];
  }

  cout << sentence << " reversed is: " << "[" << reverse << "]" << endl;

  if (sentence == reverse) {
      cout << sentence << " is a palindrome" << endl;
  } else {
    cout << sentence << " is not a palindrome" << endl;
  }
  cout << endl;
}

}

任何帮助将不胜感激。

Answer 1

问题不是Sub RemoveSmallValues() Dim myfilename As String Dim myfilepath As String Dim newfilename As String Dim N As Long Dim i As Long Dim cellvalue As Long Application.ScreenUpdating = False Application.Calculation = xlCalculationManual 'The above is just standard lines that I normally put into my code, enchances the speed of the macro. myfilepath = "C:\Snapshot.csv" myfilename = "Snapshot.csv" Workbooks.Open (myfilepath) Workbooks(myfilename).Activate 'Makes SnapShot.csv the active workbook N = Range("C1", Range("C1").End(xlDown)).Rows.Count 'counts the number of rows untill cell is BLANK, based on your code I used Column C. 'If your columns have headers then you will need to make this C2. Otherwise your headers will be included and will create a datatype error on CELLVALUE For i = 1 To N 'Again if your columns have hearders, then i will need to be i = 2 cellvalue = Cells(i, 2).Value If cellvalue <= 10000 Then Cells(i, 2).ClearContents Next i newfilename = "C:\SnapshotBB" 'new file path and file name without extension. Workbooks(myfilename).SaveAs newfilename, FileFormat:=xlCSV 'Save the file with extension CSV ActiveWorkbook.Close False 'Close the workbook without saving, as you have already saved the workbook with line before. End Sub。这就是这个部分：

if

for (int i = sentence.length(); i >= 0; i--) { reverse += sentence[i]; }是错误的，您必须从i = sentence.length()开始。否则，它似乎在字符串中添加了空格字符，从而导致错误的结果。该循环应为：

i = sentence.length()-1

请注意，根据to the documentation：

返回对指定位置pos处字符的引用。没有边界检查已执行。如果pos> size（），则行为为未定义。

因此，不能保证添加的空格，任何事情都会发生。为了获得更安全的版本，请查看at函数，如果该位置无效，则此函数将引发异常，而不是默默地引起未定义的行为。

Answer 2

字符串的结尾是length - 1，请改用它：

for (int i = sentence.length() - 1; i >= 0; --i)

Answer 3

为此替换for循环

for (int i = sentence.length()-1; i >= 0; i-- ) {

if语句无法正常工作[C ++]

3 个答案: