#include <stdio.h>
int main()
{
    void copy_string(char *from,char *to);
    char *a="I am a teacher";
    char *b="you are a student";
    printf("sting a is:%s\nstring b is :%s\n",a,b);
    copy_string(a,b);
    printf("%s,%s",a,b);
}

void copy_string(char *from,char *to)
{
    for (;*from!='\0';from++,to++)
    {
        *to=*from;
    }
    *to='\0';
}

//楼主的a、b均为字符串指针，a++,b++的概念已经与字符指针中的不同了，如果改成数组的话就对了
#include <stdio.h>
int main()
{
    void copy_string(char *from,char *to);
    char a[]="I am a teacher";
    char b[]="you are a student";
    printf("string a is:%s\nstring b is :%s\n",a,b);
    copy_string(a,b);
    printf("%s,%s",a,b);
}

void copy_string(char *from,char *to)
{
    for (;*from!='\0';from++,to++)
    {
        *to=*from;
    }
    *to='\0';
}

这是要实现连接两个字符串还是覆盖?

照你这么写
结果应该是I am a teacher,I am a teacher