方法一：

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

void my_strcpy(char *result,char *str,int len)               //複製長度為len的字串
{
	while(len)
	{
		*result = *str;
		str++;
		result++;
		len--;
	}
}

void change(char *str,char **a)
{
	int i = 0;                   //記錄行數
	int j = 0;
	int count = 0;               //記錄每行元素的個素
	char *temp = NULL;
	temp = (char*)malloc(sizeof(char));

	while(*str)
	{
		if(*str == ' '||*str == '\0')
		{
			my_strcpy(a[i],str-count,count);
			i++;
			count = 0;
		}
		count++;
		str++;
	}
	if(*str == '\0')
	{
		my_strcpy(a[i],str-count,count);
		count = 0;
		i++;
	}
	
	for(j = 0;j < i/2;j++)
	{
		strcpy(temp,a[j]);
		strcpy(a[j],a[i-j-1]);
		strcpy(a[i-j-1],temp);
	}
	for(j = 0;j < i;j++)
	{
		printf("%s ",a[j]);
	}
	printf("\n");

	free(temp);
}

int main()
{	
	int i = 0;
	char str[] = "I am from shanghai";
	char *a[4] = {0};

	for(i = 0;i < 4;i++)
	{
		a[i] = (char*)malloc(sizeof(char)*20);
	}

	change(str,a);
	
	for(i = 0;i < 4;i++)
	{
		free(a[i]);
	}
	return 0;

}
 

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

void change(char *str)
{
	char temp;
	char *p = str;
	char *start = str;
	char *end = str;

	while(*p != '\0')
	{
		p++;
		end++;
	}
	end = p-1;
	p = str;
	while(*p!='\0')
	{
		while(start < end)
		{
			temp = *start;
			*start = *end;
			*end = temp;
			start++;
			end--;
		}
		p++;
	}
}

void change1(char *str)
{
		char *p = str;
		char *start = p;
		char *end = p;
		char temp;

		while(*p != '\0')
		{
			if(*p ==' '||*p == '\0')
			{
				end = p-1;
				while(start < end)
				{
					temp = *start;
					*start = *end;
					*end = temp;
					start++;
					end--;
				}
				start = end = p+1;
			}
			p++;
		}
		end = p-1;
		while(start < end)
		{
			temp = *start;
			*start = *end;
			*end = temp;
			start++;
			end--;
		}
}

int main()
{
		char str[100];

		printf("please input string:\n");
		gets(str);

		change(str);
		change1(str);

		printf("the result is :%s\n",str);
}