不使用庫函數，實現 strcpy，strcat，strcmp

strcpy原型：

char* strcpy(char* des,const char* source)
{
	char* r = des;
	assert((des != NULL) && (source != NULL));
	while((*r++ = *source++)!='\0');
	return des;
}

自行實現：

char* myStrcpy(char* dest, char* src)
{
	char* r = dest;
	if (dest == NULL || src == NULL)
		return NULL;

	while ((*r++ = *src++) != '\0');
	return  dest;
}