求助 C 中的一个小问题

#include <stdio.h>
#include <curses.h>

int main()
{
        void copy_string(char from[], char to[]);
        char a[] = "I am a teacher";
        char b[] = "you my student";
        char * from = a, * to = b;
        printf("string a = %s\n string b = %s\n",a,b);
        printf("\ncopy string a to string b:\n");
        copy_string(from, to);
        printf("string a = %s\nstring b = %s\n",a,b);
        return 0;
}

void copy_string(char from[],char to[])
{
        int i = 0;
        while(from[i]!='\0')
        {
                to[i++]=from[i++];
        }
        to[i]='\0';
}

第一段输出结果为：

string a = I am a teacher
string b = you my student

copy string a to string b:
string a = I am a teacher
string b = om aytsauhert

#include <stdio.h>
#include <curses.h>

int main()
{
        void copy_string(char from[], char to[]);
        char a[] = "I am a teacher";
        char b[] = "you my student";
        char * from = a, * to = b;
        printf("string a = %s\n string b = %s\n",a,b);
        printf("\ncopy string a to string b:\n");
        copy_string(from, to);
        printf("string a = %s\nstring b = %s\n",a,b);
        return 0;
}

void copy_string(char from[],char to[])
{
        int i = 0;
        while(from[i]!='\0')
        {
                to[i]=from[i];
                i++;
        }
        to[i]='\0';
}

想请教的问题是：

      to[i]=from[i];
      i++;

改成了

      to[i++]=from[i++];

之后为什么结果是不对的？