指针强大,字符串复制连接包含运算，

#include
#include

/*
等价于
void stringcopy(char *source, char *target)
{
    int i=0;
    while((source[i] = target[i]) != '\0')
        i++;
}
*/
void  strcpy(char * source,char * des)
{

    while(*des++ = *source++);//先赋值再自增
}


void strcat(char * from,char * to)
{
    while(*from)
        from++;
    while(*from++=*to++);

}
int main()
{
    char str_a[] = "Welcome to ";
    char str_b[] = "";
    strcpy(str_a,str_b);
    printf("%s\n",str_b);

    char str_c[]="hello ";
    char srr_d[]="world!";
    strcat(str_c,srr_d);
    printf("%s\n",str_c);

    return 0;
}
Welcome to
hello world!
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