现在时间
#include<iostream> #include<ctime> using namespace std; int main() { int totalSeconds = time(0); int CurrentSecond = totalSeconds%60; int totalMinutes = totalSeconds/60; int CurrentMinutes = totalMinutes%60; int totalHours = totalMinutes/60; int CurrentHours = (totalHours+8)%24; cout << "Current time is " << ":" << CurrentHours << ":" << CurrentMinutes << ":" << CurrentSecond << "GMT" << endl ; system("pause"); return 0; }
布尔值不必再测试
if （even == true）---------if （even）
常见错误 两浮点值的相等性测试
浮点有精度限制 一旦涉及计算 就会导致舍入，所以 要用数学表达
非常接近
就是||<epsilon
减法练习
#include<iostream> #include<ctime> #include<cstdlib>//for rand and srand fuction using namespace std; int main() { srand(time(0)); int number1 = rand() % 10; int number2 = rand() % 10; if (number1 < number2) { int temp = number1; number1 = number2; number2 = temp; } cout << "题目是：" << number1 << "-" << number2 << endl << " 你的答案是："; int ans; cin >> ans; if(ans == number1 - number2) cout << "yes！"; else cout << "wrong!"; system("pause"); return 0; }
十六进制转十进制
#include<iostream> #include<cctype>//测试和转换字符 using namespace std; int main() { cout << "enter a digit :"; char hexDigit; cin >> hexDigit; hexDigit = toupper(hexDigit);//daxie if (hexDigit <= 'F' && hexDigit >= 'A') { int value = 10 + hexDigit - 'A'; cout << hexDigit << "is" << value; } system ("pause"); }
String 是一个对象类型
// Forward declarations -- C++ -- // Copyright © 2001-2018 Free Software Foundation, Inc. // // This file is part of the GNU ISO C++ Library. This library is free // software; you can redistribute it and/or modify it under the // terms of the GNU General Public License as published by the // Free Software Foundation; either version 3, or (at your option) // any later version. // This library is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // Under Section 7 of GPL version 3, you are granted additional // permissions described in the GCC Runtime Library Exception, version // 3.1, as published by the Free Software Foundation. // You should have received a copy of the GNU General Public License and // a copy of the GCC Runtime Library Exception along with this program; // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see // http://www.gnu.org/licenses/. /** @file bits/stringfwd.h This is an internal header file, included by other library headers. Do not attempt to use it directly. @headername{string} */ // // ISO C++ 14882: 21 Strings library //
写入文件
#include<iostream> #include<fstream> using namespace std; int main() { ofstream output; output.open("numbers.txt"); output << 95 <<" "<< 56 << " " << 88; output.close(); cout << "Done" << endl; system ("pause"); }
const int NUMBER_OF_QUESTIONS = 5;
输入和输出重定向–键盘输入太过于笨拙 Sentinel value.exe > output.txt
#include<iostream> #include<fstream> using namespace std; int main() { ifstream input("numbers.txt"); double sum = 0; double number; while(!input.eof()) { input >> number; cout << number <<" " ; sum += number; } input.close(); cout << "Done" << sum << endl; system ("pause"); }
函数—和c一致
和c一致
–传值方式
函数的重载–同名不同参数
函数原型 prototype – int max （int num1， int num2）后面再实现
缺省参数–设置一个缺省值 --默认值 int max （int num1 ，int num2=5）–只能后面的缺省
内联函数-提高性能-避免函数调用压栈的开销
inline void f(int a) { cout << a; }
static int x = 1；— 会一直驻留在内存
引用传参-特殊变量 引用变量
int& a; #include<iostream> using namespace std; void swap(int& num1,int& num2) { int temp; temp = num1; num1 = num2; num2 = temp; } int main() { int num1=1,num2=2; cout << num1 << " " << num2 <<endl; swap(num1, num2); cout << num1 << " " << num2; system ("pause"); }
常量引用传递 int max （const int& num1）—不可改变
设置桩函数–自顶向下设计—逐步求精
一维数组array和C字符串
shuffling 洗牌 数组—数组 天生的 引用传递
#include<iostream> #include<ctime> using namespace std; void shuffling(int team[], int arraySize) { srand(time(0)); for(int i=arraySize-1; i>0; i--) { int j = rand()%(i + 1); int temp = team[i]; team[i]=team[j]; team[j]=temp; } } int main() { int team[100]; for(int i = 0; i < 100 ; i ++ ) { team[i] = i; } shuffling(team, 100); for(int i = 0; i < 100 ; i ++ ) { cout << team[i] << " "; } system("pause"); }
防止数组修改 void f（ const int list【】，int arraySize）
数组作为返回值–反转array
#include<iostream> #include<ctime> using namespace std; void reverse(int team[],int newteam[],int size){ for(int i=0,j=size-1;i<size;i++,j--){ newteam[j]=team[i]; } } void printArray(int team[], int size){ for(int i = 0; i < 100 ; i ++ ) { cout << team[i] << " "; } } int main() { int team[100]; int newteam[100]; for(int i = 0; i < 100 ; i ++ ) { team[i] = i; } reverse(team, newteam, 100); printArray(newteam,100); system("pause"); }
二分搜索
#include<iostream> #include"ShufflingArray.cpp" using namespace std; void reverse(int team[],int newteam[],int size){ for(int i=0,j=size-1;i<size;i++,j--){ newteam[j]=team[i]; } } void printArray(int team[], int size){ for(int i = 0; i < 100 ; i ++ ) { cout << team[i] << " "; } } int binarySearch(int team[],int size,int key) { int low=0,high=size-1; while(low<=high) { int mid=(low+high)/2; cout << low << " " << mid << " "<< high<< endl; if(team[mid]>key){ high=mid-1; } else if (team[mid == key]){ return mid; } else{ low=mid+1; } } return -1; } int main() { int team[100]; int newteam[100]; for(int i = 0; i < 100 ; i ++ ) { team[i] = i; } shuffling(team,100); int key = 33; int a = binarySearch(team,100,key); cout << a; //reverse(team, newteam, 100); //printArray(newteam,100); system("pause"); }
选择排序
#include<iostream> #include"ShufflingArray.cpp" using namespace std; void printArray(int team[], int size){ for(int i = 0; i < 100 ; i ++ ) { cout << team[i] << " "; } } void selectionSort(int team[], int size){ for(int i = 0; i < size ; i ++ ) { int currentMin = team[i]; int currentMinIndex = i; for(int j = i + 1 ; j < size ; j ++) { if(currentMin > team[j]){ currentMin = team[j]; currentMinIndex = j; } } if(currentMinIndex != i) { team[currentMinIndex] = team[i]; team[i] = currentMin; } } } int main() { int team[100]; for(int i = 0; i < 100 ; i ++ ) { team[i] = i; } shuffling(team,100); selectionSort(team,100); printArray(team,100); system("pause"); }
c的字符串 string—结尾是’\0’
itoa（）
二维数组做参数----------需要a【】【column_size】–
#include <iostream> #include <cmath> using namespace std; double getDistance(double x1, double y1, double x2, double y2) { return sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)); } int main() { const int NUMBER_OF_POINTS = 8; double points[NUMBER_OF_POINTS][2]; cout << "Enter " << NUMBER_OF_POINTS << " points:"; for (int i = 0; i < NUMBER_OF_POINTS; i ++) { cin >> points[i][0] >> points[i][1]; } int p1=0,p2=1; double shortestDistance = getDistance(points[p1][0], points[p1][1] , points[p2][0], points[p2][1]); for (int i = 0; i < NUMBER_OF_POINTS; i++) { for (int j = i+1; j < NUMBER_OF_POINTS; j++) { double distance = getDistance(points[i][0], points[i][1] , points[j][0], points[j][1]); if(shortestDistance > distance) { shortestDistance = distance; } cout << shortestDistance; } } cout << "shortest:" << shortestDistance; system("pause"); // 防止运行后自动退出，需头文件stdlib.h return 0; }
对象和类
初始化列表来初始化数据域
Circle ：：Circle（） ：radius（1） { }
Circle ：：Circle（） { radius = 1； }
类定义实现分离
。h ---------意味 头head
相同名字 不同扩展名
：：二元作用域解析符号 -binary scope resolution operator
如 std ：：cout<< “hello”;
避免多次包含-包含保护 inclusion guard
类中的 内联函数—内联定义
面对对象思想
数字转字符串 ss.str()
类的设计–内聚 。。。
指针 动态内存管理–原来如此 为什么当初我的老师要这样教我，让我产生如此巨大的误解！-指针也不过是个变量 用四个字节存一个地址
#include<iostream> using namespace std; int main() { int count = 5; int* pCount = &count; cout << count <<endl; cout << pCount<<endl; cout << &count << endl; cout << *pCount << endl; system ("pause"); }
#include<iostream> using namespace std; int main() { int count = 5; int* pCount = &count;//*用于声明 cout << count <<endl; cout << pCount<<endl; cout << &count << endl; cout << *pCount << endl;//*用于解引用 system ("pause"); }
常量数据 常量指针
const double* const pValue = &radius；
数组名实际上是 指向数组第一个元素的常量指针
指针从 list +0 开始 所以数组下标从0开始
指针交换
#include<iostream> using namespace std; void swap3(int* p1, int* p2)//交换指针的值 { int temp = *p1; *p1 = *p2; *p2 = temp;//把指针指向的变量换了 } int main() { int num1 = 1; int num2 = 2; swap3(&num1,&num2);//传进去指针变量 cout << num1 << num2; system ("pause"); }
动态持久内存分配//局部变量在栈中 new分配在堆中–动态数组
#include<iostream> using namespace std; int* reverse(const int* list,int size) { int* result = new int[size]; for (int i = 0 , j=size-1; i < size ; i++,j--) { result[i]=list[j]; } return result; } void printArray(int team[], int size){ for(int i = 0; i < size ; i ++ ) { cout << team[i] << " "; } } int main() { int list[]={1,2,3,4,5,6}; int* p = reverse(list, 6);//动态数组：int* list =new int【size】； printArray(p, 6); system ("pause"); }
this指针—指向被调用对象本身-访问被屏蔽的数据域–局部变量同名，所以屏蔽对象本身的变量
访问被屏蔽的数据域
析构函数destructor
每个类都有一个析构函数 ， 当一个对象销毁时候自动调用该析构函数
delete circle1；
模板、向量、栈
模板栈
template<class T> class Stack { private: class Node { public: T x; Node* next; Node(){} Node(T t,Node* next){ this->x = t; this->next = next; } Node(Node& node){ this->x = node.x; this->next = node.next; } }; Node* top; int num; public: Stack(){ top = new Node(0,nullptr); num = 0; } ~Stack(){ while(top->next!=nullptr){ Node* temp = top->next; top->next = top->next->next; delete temp; } delete top; num = 0; } void push(T t){ Node* oldfirst = top->next; Node* newfirst = new Node(t,nullptr); newfirst->next = oldfirst; top->next = newfirst; num++; } T pop(){ if(top->next!=nullptr){ Node* temp = top->next; top->next = top->next->next; T val = temp->x; delete temp; num--; return val; } } int getlength(){ return num; } };
向量类vector–更灵活vector intVector（10）； 使用intVector【0】=5；要保证里面有元素！
#include<iostream> #include<vector> #include<string> using namespace std; int main() { vector<int> intVector; for(int i = 0; i<3;i++) intVector.push_back(i+1); cout << intVector[0]; vector<string> stringVector; stringVector.push_back("Dalao"); cout << stringVector[0]; system ("pause"); }
向量表示二维数组
#include<iostream> #include<vector> using namespace std; int main() { vector<vector<int> > matrix(4); for(int i = 0; i<4;i++) matrix[i]=vector<int>(3); matrix[0][0]=1; system ("pause"); }
