问题引入

将一句话的单词进行倒置,标点不倒置.比如 I like beijing. 经过函数后变为：beijing. like I
输入描述:
每个测试输入包含1个测试用例： I like beijing. 输入用例长度不超过100
输出描述:
依次输出倒置之后的字符串,以空格分割: beijing. like I

一、思路

• The entire sentence can be reversed first,Reverse the order of each word;You can also reverse each word first,Reverse the entire sentence.
• Custom reverse order functionreverse(),无返回值;Its parameter list is put into the address of the beginning and end of the word or sentence that needs to be reversed（char* left, char* right）;The function body uses a loop,An object that constantly exchanges head and tail addresses,每交换一次,The first address will be respectively+1,尾地址-1,Until the first address is greater than the last address, the exchange condition is not satisfied,交换结束.
• Find the address of the beginning and end of each word：First set the first and last addresses to the first address of the arrayarr,Next traverse the tail addressend,until the trailing address is a space,Indicates the end of the first word,The trailing address is the one before the space,即end-1;此时,The first address is updated to the one after a space,即end+1;以此循环,直到遍历到‘\0’（字符串结束标志）End the loop at the end of the sentence.按此方法,You can get the start and end addresses of each word.
• Find the address of the beginning and end of the entire sentence：The first address is the first address of the arrayarr,The tail address is the first address plus the length of the array minus one.

二、代码展示

代码如下：

#include <stdio.h>
#include<string.h>
#include<assert.h>
void reverse(char* left, char* right) {
    
	assert(left);
	assert(right);
	while (left < right) {
    
		char temp = *left;
		*left = *right;
		*right = temp;//Object to exchange the first address
		left++;
		right--;
	}
}
int main() {
    
	char arr[101] = {
     0 };
	gets(arr);
	char* cur = arr;//定义指针变量cur存储arr首地址
	while (*cur) {
    //cur='\0'结束循环
		char* start = cur;//定义start指针变量
		char* end = cur;//定义end指针变量
		while (*end != ' ' && *end != '\0') {
    //endTraverse until a space or end of sentence stops
			end++;
		}
		//对每个单词进行逆序
		reverse(start, end - 1);
		if (*end !='\0') {
    
			cur = end + 1;//首地址cur更新
		}
		else {
    
			cur = end;//cur='\0'
		}
	}
	
	int len = strlen(arr);//计算数组长度
	//Reverse the entire sentence
	reverse(arr, arr + len - 1);
	//输出
	printf("%s\n", arr);
	return 0;
}

speculative method

• The method uses recursion,Put it first each time a string is readarrdoes not print in,Then print backwards when the recursion goes back.
• 弊端：This method just reverses the output of the string by reading,Essentially the string is not stored for inversion.

代码如下：

#include<stdio.h>
void reverse() {
    
	char *arr[101];
	if (scanf("%s",arr)!= EOF) {
    
		reverse();
		printf("%s ", arr);
	}
}
int main() {
    
	reverse();
	return 0;
}

提示：The first method is generally recommended,The second method only understands,Avoid errors in use in other situations！There are other ideas and methods can also be exchanged,有错误的地方欢迎指正.