Question

我正在尝试使用我在python中学到的东西在C中做一个回文检查...（我是这里的新手）。回文检查器从文件中获取输入，直到它读取文件的位置，那里没有问题，但我不确定输出是否表示所有单词（来自输入文件）的确切问题不是回文.....

#include <stdio.h>
#include <string.h>
#include <stdlib.h>


void palinChecker(char *input);
void main()
{
   FILE *fp;
   char buff[255];

   fp = fopen("input.txt", "r");
   if( fp != NULL ){
      while ( !feof(fp ) ){
         memset(buff, '\0', sizeof( buff) );
         fgets(buff, 255, (FILE*)fp);

         palinChecker(buff);
      }
      fclose(fp);
   }
}

void palinChecker(char *input){
    int i, index=0;
    char letter;
    char rev[255];
    size_t length = strlen(input);
    int n = length-2;

    while(index<n){
        letter = input[n-1];
        rev[index] = letter;
        index = index + 1;
        n = n - 1;
    }
    if(rev == input){
        printf("%s is a palindrome\n", input);
    }
    else{
        printf("%s is not a palindrome\n", input);
    }
}

请我不知道为什么结果如此...... 结果：

ABA 不是回文

kanakanak 不是回文

KANAKANAK 不是回文

11 不是回文

ZZ 不是回文

12321 不是回文

012345678909876543210 不是回文

abcdefghijklmnopqrstuvwxyzzyxwvutsrqponmlkjihgfedcba 不是回文

llllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll不是回文结构

升不是回文

计算机不是回文

科学不是回文

阿巴不是回文

Kanakanak 不是回文

123 不是回文

llllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll11llllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll不是回文结构

l不是回文

Answer 1

除了在C中，你不能将字符串与==进行比较（你必须使用strcmp），你的算法有一个缺陷。让我们在input =“aba”的情况下走下去：

void palinChecker(char *input){      // "aba"
    int i, index=0;
    char letter;
    char rev[255];
    size_t length = strlen(input);    // 3
    int n = length-2;                 // 1

    while(index<n){                    // index = 0 in the beginning, n = 1
        letter = input[n-1];           // letter = input[0] = 'a'
        rev[index] = letter;           // rev[0] = 'a'
        index = index + 1;             // index = 1
        n = n - 1;                     // n = 0
    }                                  // ...and we get out of the cycle
    if(rev == input){                  // rev = "a" (not 0-terminated), input = "aba"
        printf("%s is a palindrome\n", input);
    }
    else{
        printf("%s is not a palindrome\n", input);
    }
}

Answer 2

如上所述，您使用相等运算符（==）来比较2个字符串。这是错误的，因为在C中，字符串存储为字符数组。字符串的名称是指向该数组的第一个元素的指针（指针是一个具有内存地址作为值的变量）。因此，在C中，指定字符串的变量不包含有关字符串的任何数据，这与python不同。因此，当您进行比较时，您基本上比较了2个内存地址。由于存在2个不同的字符串，存储在不同的地方，所以相等性总是为假。

为避免这种情况，C标准库提供了strcmp函数（在strings.h中）。传递要作为参数进行比较的字符串，如果第一个字符串更大则结果为正，如果第一个字符串更小则结果为负，如果字符串相等则结果为0.

在C做一个回文检查

2 个答案: