void strcopy(char *d, char *s){
    printf("Start copying.\n");
    while(*s!='\0'){
        printf("Copying.\n");
        *d = *s;
        d+=1;
        s+=1;
    }
}
int main()
{
    char *a = "abcd" ,*b = "efgh";
    strcopy(a,b);
    printf("a:%s, b:%s\n", a,b);
    return 0;
}