更改字符串中某些单词的顺序

Question

我已经尝试解决这个练习一周了，但我的代码不起作用，我不明白为什么以及如何更改它。练习是:从用户处接收一个长度，然后从用户处接收一个与“length”一样长的字符串(str)，然后从用户处接收一个数字(int n)。然后我需要执行函数 'void ReverseNumWords (char*str, int n) ).该函数反转字符串中的前n个单词。例如:对于“我是你的父亲星球大战”且 n=3:“你是我的星球大战之父”。假设这些单词是用 ' ' 分隔的，这是正确的。谢谢您的帮助!!

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

void Reverse()
{

   int len,num;
   char *str;
   printf("Please enter how many chars to allocate:\n");
   //Asking from the user the length of a string.
   scanf("%d", &len);
   //Allocating memory for the string.
   str = (char*)calloc(len, sizeof(int));
   //Making sure the allocation was successful.
   if (!str)
       printf("Error: Cannot allocate Memory\n");
   printf("Allocated %d chars\n", len);
   printf("Please enter your string:\n");
   scanf("%s", str);
   printf("Please enter how many words to reverse:\n");
   scanf("%d", &num);
   ReverseNumWords(*str, num, len);
   free(str);
}

void ReverseNumWords(char*str, int num,int len)
{

   char *sub;
   char temp;
   //Allocating memory for the string.
   sub = (char*)calloc(len, sizeof(int));
   //Making sure the allocation was successful.
   if (!sub)
       printf("Error: Cannot allocate Memory\n");
   int i, j,l;
   i = j = 0;
   for (; i < len, j <= num; i++)
       if (str[i] == '\0' || str[i] == 0)
           j++;

   for (l = 0; l < i; l++)
       sub[i] = str[i];

   for (j = 0; j < i; j++)
       temp = sub[j];
       sub[j] = sub[i - (1+j)];
       sub[i - (1+j)] = sub[j];

   reverseWords(*sub);


}

void reverseWords(char *sub)
{

   char *word_begin = sub;
   char *temp = sub;

   while (*temp)
   {
      temp++;
      if (*temp == '\0')
      {
         reverse(word_begin, temp - 1);
      }
      else if (*temp == ' ')
      {
         reverse(word_begin, temp - 1);
         word_begin = temp + 1;
      }
   } 

   reverse(sub, temp - 1);
}

void reverse(char *begin, char*sub, char *end)
{

    char temp;
    while (begin < end)
    {
        temp = *begin;
        *begin++ = *end;
        *end-- = temp;
    }
    printf("%s\n", sub);
}

Answer 1

你的读取函数应该是这样的

int len,num;
   char *str;
   printf("Please enter how many chars to allocate:\n");
   //Asking from the user the length of a string.
   scanf(" %d", &len);
   //Allocating memory for the string.
   str = (char*)malloc(sizeof(char)*(len+1));
   //Making sure the allocation was successful.
   if (!str)
       printf("Error: Cannot allocate Memory\n");

   printf("Allocated %d chars\n", len);
   printf("Please enter your string:\n");
   scanf(" %[^\n]s", str);

   printf("Please enter how many words to reverse:\n");
   scanf(" %d", &num);
   ReverseNumWords(*str, num, len);
   free(str);

因为使用 %s 读取时，您将停在找到的第一个“”(空格)处。并且您想要阅读直到找到\n(输入)。