C++ 面向对象学习笔记[1]

#include <cassert>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

int RandomGenerator(int max) {
  assert(max <= RAND_MAX);
  srand(time(NULL));
  int a = rand() % max;
  return a;
}

enum Fruit {
  apple,
  banana,
  pear,
  orange,
  watermelon, // the , is not necessary
};

class Simple {
private:
  int num;

public:
  Simple(int a) { num = a; };
  int get() { return num; };
};

struct BigInteger {
  static const int BASE = 100000000;
  static const int WIDTH = 8;
  vector<int> s;

  BigInteger(long long num = 0) { *this = num; }
  BigInteger operator=(long long num) {
    s.clear();
    do {
      s.push_back(num % BASE);
      num /= BASE;
    } while (num > 0);
    return *this;
  }

  BigInteger operator=(const string &str) {
    s.clear();
    int x, len = (str.length() - 1) / WIDTH + 1;
    for (int i = 0; i < len; i++) {
      int end = str.length() - i * WIDTH;
      int start = max(0, end - WIDTH);
      sscanf(str.substr(start, end - start).c_str(), "%d", &x);
      s.push_back(x);
    }
    return *this;
  }
};

BigInteger a;
Fruit c = apple; // can without init
Simple b(100);   // = and () both okay
int main() {
  a = 12345123;
  cout << b.get();
}

• 关于auto关键字：
  • 　　在C++11前：意味着auto detect GC time，跟内存回收有关系
  •        在C++11    ：意味着自动判断变量类型(或函数返回类型)
    •      演示

      auto a = 1.0; // 自动判断类型 a 是一个double
      auto a;//错误，a不能未加初始化
      int compare(auto a,auto b);//错误，auto无法根据上下文推断
      auto compare(int a,int b);//错误，auto无法根据上下文推断
      auto compare(int a,int b) -> int;//正确，但这种用途仅为了美观

  •          在C++11后 ： 另有变更，此处不讨论
• 关于*this: http://www.learncpp.com/cpp-tutorial/8-8-the-hidden-this-pointer/