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   "source": [
    "# C++的谓词"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 1. 简介"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "① 返回bool类型的仿函数称为谓词。\n",
    "\n",
    "② 如果operator()接受一个参数，那么叫做一元谓词。\n",
    "\n",
    "③ 如果operator()接受两个参数，那么叫做二元谓词。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 2. 一元谓词"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "#include<iostream>\n",
    "using namespace std;\n",
    "#include<vector>\n",
    "#include<algorithm>\n",
    "\n",
    "//仿函数 返回值类型是bool数据类型，称为谓词\n",
    "//一元谓词\n",
    "class GreaterFive\n",
    "{\n",
    "public:\n",
    "    bool operator()(int val)\n",
    "    {\n",
    "        return val > 5;\n",
    "    }\n",
    "};\n",
    "\n",
    "void test01()\n",
    "{\n",
    "    vector<int>v;\n",
    "    for (int i = 0; i < 10; i++)\n",
    "    {\n",
    "        v.push_back(i);\n",
    "    }\n",
    "\n",
    "    //查找容器中，有没有大于5的数字\n",
    "    //GreaterFive() 匿名函数对象\n",
    "    vector<int>::iterator it = find_if(v.begin(), v.end(), GreaterFive());\n",
    "    if (it == v.end())\n",
    "    {\n",
    "        cout << \"未找到\" << endl;\n",
    "    }\n",
    "    else\n",
    "    {\n",
    "        cout << \"找到大于5的数字为：\" << *it << endl;\n",
    "    }\n",
    "}\n",
    "\n",
    "int main() \n",
    "{\n",
    "    test01();\n",
    "    \n",
    "    system(\"pause\");\n",
    "\n",
    "    return 0;\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "运行结果： \n",
    " - 找到大于5的数字为：6\n",
    " - 请按任意键继续. . ."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 3. 二元谓词"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "#include<iostream>\n",
    "using namespace std;\n",
    "#include<vector>\n",
    "#include<algorithm>\n",
    "\n",
    "//仿函数 返回值类型是bool数据类型，称为谓词\n",
    "//二元谓词\n",
    "class MyCompare\n",
    "{\n",
    "public:\n",
    "    bool operator()(int val1,int val2)\n",
    "    {\n",
    "        return val1 > val2;\n",
    "    }\n",
    "};\n",
    "\n",
    "void test01()\n",
    "{\n",
    "    vector<int>v;\n",
    "    v.push_back(10);\n",
    "    v.push_back(40);\n",
    "    v.push_back(50);\n",
    "    v.push_back(20);\n",
    "    v.push_back(30);\n",
    "\n",
    "    sort(v.begin(), v.end());\n",
    "    for (vector<int>::iterator it = v.begin(); it != v.end(); it++)\n",
    "    {\n",
    "        cout << *it << \" \";\n",
    "    }\n",
    "    cout << endl;\n",
    "\n",
    "    //使用函数对象，改变算法策略，变为排序规则为从大到小\n",
    "    sort(v.begin(), v.end(), MyCompare());  //MyCompare()为函数对象，是匿名函数\n",
    "\n",
    "    cout << \"----\" << endl;\n",
    "    for (vector<int>::iterator it = v.begin(); it != v.end(); it++)\n",
    "    {\n",
    "        cout << *it << \" \";\n",
    "    }\n",
    "    cout << endl;\n",
    "}\n",
    "\n",
    "int main() {\n",
    "\n",
    "    test01();\n",
    "\n",
    "    system(\"pause\");\n",
    "    \n",
    "    return 0;\n",
    "\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "运行结果：  \n",
    " - 10 20 30 40 50\n",
    " - $----$\n",
    " - 50 40 30 20 10\n",
    " - 请按任意键继续. . ."
   ]
  }
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