Ｃ++笔记之零碎点
1，测试cin.ignore（）的作用，用于去除缓冲区的残留数据
1 #include <iostream> 2 3 int main() 4 { 5 char buff[20]; 6 char buff1[20]; 7 8 std::cin >> buff1; 9 std::cin.ignore(7, '\n'); // 通常把获取前n个字符写的很大，去掉前一次输入的‘\n’ 10 std::cin.getline(buff, 10); // 只能获取９个，存最末尾储'\0' 11 12 std::cout << buff << std::endl; 13 14 return 0; 15 }
2.整形的占用位数
1 #include <iostream> 2 #include <climits> 3 4 int main() 5 { 6 using namespace std; 7 8 int n_int = INT_MAX; 9 short n_short = SHRT_MAX; 10 long n_long = LONG_MAX; 11 long long n_llong = LLONG_MAX; 12 13 cout << "int : " << sizeof n_int << "bytes." << endl; 14 cout << "short : " << sizeof n_short << "bytes." << endl; 15 cout << "long : " << sizeof n_long << "bytes." << endl; 16 cout << "long long: " << sizeof n_llong << "bytes." << endl; 17 cout << endl; 18 19 cout << "Maximum values:" << endl; 20 cout << "int : " << n_int << endl; 21 cout << "short : " << n_short << endl; 22 cout << "long : " << n_long << endl; 23 cout << "long long: " << n_llong << endl; 24 25 }
运行结果：
int : 4bytes.
short : 2bytes.
long : 8bytes.
long long: 8bytes.
Maximum values:
int : 2147483647
short : 32767
long : 9223372036854775807
long long: 92233720368547758073，整形溢出
4，cin的相关方法 - ignore，get，getline，peek，gcount，read
1 #include <iostream> 2 #include <climits> 3 using namespace std; 4 int main() 5 { 6 const int SIZE = 50; 7 char buff[SIZE]; 8 9 cout << "请输入一段文本："; 10 cin.read(buff, 10); //读取输入，阻塞计数，不忽略回车 11 12 cout << "输入的文本字符数为：" << cin.gcount() << endl; //统计 13 14 cout << "输入的文本信息是："; 15 cout.write(buff, 19); //读取缓冲区数据，打印 16 cout << endl; 17 18 return 0; 19 20 }
运行结果：
请输入一段文本：yfu
67t
87y
输入的文本字符数为：10
输入的文本信息是：yfu
67t
85，文件复制
此处换行符会被过滤掉，所以逐行读取，手动添加ENDL。
1 #include <iostream> 2 #include <climits> 3 #include <fstream> 4 5 using namespace std; 6 int main() 7 { 8 ifstream in; //文件输入流类对象 9 in.open("../test.txt", ios::binary); //用两种方法来打开文件 10 ofstream out("../test1.txt", ios::binary | ios::app); //文件输出流类对象 11 12 if(!in){ 13 cerr << "打开文件失败" << endl; 14 return 0; 15 } 16 17 // char x; 18 // while( in >> x){ 19 // if(x != '\n'){ 20 // cout << x; 21 // out << x; 22 // } 23 // else{ 24 // cout << "遇到换行"; 25 // out << "-------********\n"; 26 // } 27 28 in.seekg(ios::beg); //指针指向文件头 29 30 for(string s; getline(in, s);){ 31 cout << s << endl; 32 out << s << endl; 33 } 34 35 cout << endl; 36 37 in.close(); 38 out.close(); 39 40 return 0; 41 }
6，输入输出，切换循环
1 #include <iostream> 2 3 int main() 4 { 5 char answer; 6 7 std::cout << "请问你毕业了吗？[Y/N]" << std::endl; 8 std::cin >> answer; 9 10 switch(answer){ 11 case 'Y': 12 case 'y': 13 std::cout << "你毕业了！" << std::endl; 14 break; 15 16 case 'N': 17 case 'n': 18 std::cout << "你怎么还没有毕业！" << std::endl; 19 break; 20 21 default: 22 std::cout << "输入不符合要求！！！" << std::endl; 23 break; 24 } 25 26 std::cin.ignore(100, '\n'); 27 28 std::cout << "输入任何字符结束" << std::endl; 29 std::cin.get(); 30 31 }
如图7所示，温度转换（我写的第一个C ++程序）
1 #include <iostream> 2 3 int main() 4 { 5 // 输入选择，确定公式 6 char answer; 7 std::cout << "请问待转换的温度单位序号：\n" 8 << "1. 华氏度(℉) \n" 9 << "2. 摄氏度(℃) " << std::endl; 10 std::cin >> answer; 11 12 // 输入温度值 13 float temperature; 14 std::cout << "请输入当前温度：" << std::endl; 15 std::cin.ignore(100, '\n'); 16 std::cin >> temperature; 17 18 // 进行判断，输出结果 19 float f2c(float num); 20 float c2f(float num); 21 float result = -1000; 22 23 switch(answer){ 24 case '1': 25 result = f2c(temperature); 26 break; 27 case '2': 28 result = c2f(temperature); 29 break; 30 default: 31 std::cout << "输入不符合要求！！！" << std::endl; 32 break; 33 } 34 35 if(result != -1000){ 36 std::cout << result << std::endl; 37 } 38 else{ 39 std::cout << "输入错误" << std::endl; 40 } 41 42 } 43 44 float f2c(float num){ 45 // 摄氏度 = 【(华氏度 - 32) ÷ 1.8】℃ 46 float result; 47 48 result = (num-32) ; 49 result /= 1.8; 50 51 return result; 52 } 53 54 float c2f(float num){ 55 // 华氏度 = (32 + 摄氏度 × 1.8)℉ 56 float result; 57 58 num *= 1.8 ; 59 result = num + 32; 60 61 return result; 62 }
手痒写一个Python的版本：
1 temper = input('请输入温度，形如【23.2 C】或者【23.2 F】') 2 temp_value, temp_type = temper.split(' ') 3 4 temp_value = float(temp_value) 5 temp_type = temp_type.upper() 6 7 print(temp_type, temp_value) 8 if (temp_type == 'C') : 9 result = str(round(temp_value*1.8 + 32, 2)) + '℉' 10 elif(temp_type == 'F') : 11 result = str(round((temp_value-32)/1.8, 2)) + '℃' 12 else: 13 result = None 14 print('输入有误') 15 16 print(result)
8.地址运算符和间接值运算符的使用
运行结果如下：
Values: updates = 6, *p_updates = 6
Addresses: &updates = 0x7ffd2f82ce0c, &p_updates = 0x7ffd2f82ce0c可见，对变量名对应地址取间接运算符，相当与获得变量名对应值。
9.数组的指针地址
1 #include<iostream> 2 #include<string> 3 #include <limits> 4 5 int main() 6 { 7 const unsigned short ITEMS = 5; 8 9 int intArray[ITEMS] = {1, 2, 3, 4, 5}; 10 char charArray[ITEMS] = {'f', 'I', 'j', 'K', ';'}; 11 12 int *intPtr = intArray; 13 char *charPtr = charArray; 14 15 //显示整形数组的内存地址 16 std::cout << "整型数组输出：" << '\n'; 17 for (int i = 0; i < ITEMS; i++) { 18 std::cout << *intPtr << " at " << reinterpret_cast<unsigned long>(intPtr) << std::endl; 19 intPtr++; 20 } 21 22 //显示字节型数组的内存地址和指针对打印的影响 23 std::cout << "字符型数组输出：" << '\n'; 24 for (int i = 0; i < ITEMS; i++) { 25 std::cout << *charPtr << " at " << reinterpret_cast<unsigned long>(charPtr) << " - " << charPtr << std::endl; 26 charPtr++; 27 } 28 29 //测试运算 30 int *temp = intArray; 31 std::cout << *temp+1<< std::endl; 32 std::cout << *(temp+1) << std::endl; 33 return 0; 34 };
9.字符串指针，动态创建
1 #include <iostream> 2 #include <string> 3 4 using namespace std; 5 6 int main() 7 { 8 const int num = 5; 9 10 string temp; 11 auto *plist = new string [num]; 12 13 for (int i = 0; i<num; i++) { 14 cout << "请输入第" << i+1 << "个字符" << endl; 15 cin >> temp; 16 17 plist[i] = temp; 18 } 19 20 cout << plist->length() << endl; //4个字节，64位系统 21 22 for (int i = 0; i<num; i++) { 23 cout << plist << " --- " << plist[0] << endl; //不是plist[i] 24 plist ++; //指针加法，指向下一个字符 25 } 26 27 }
10.输出阶乘
#include <iostream> #include <string> using namespace std; struct student{ char age[20]; char gender[20]; string name; }; const int Arsize = 16; int main() { long long factor[Arsize]; factor[0] = factor[1] = 1LL; for (int i = 2; i<Arsize; i++) { factor[i] = factor[i-1] *i; } for (long long i : factor) { cout << i << "! = " << i << endl; } }
11. 枚举和switch的组合使用
1 #include <iostream> 2 #include <string> 3 #include <vector> 4 5 using namespace std; 6 7 enum { 8 red, orange, yellow, green, blue, violet, indigo 9 }; 10 11 int main() { 12 cout << "请输入你的选择(0-6): \n"; 13 14 int code; 15 16 while (cin >> code && code >= 0 && code <= 6) { 17 switch (code) { 18 case red: 19 cout << 0 << endl; 20 break; 21 case orange: 22 cout << 1 << endl; 23 break; 24 case yellow: 25 cout << 2 << endl; 26 break; 27 case green: 28 cout << 3 << endl; 29 break; 30 case blue: 31 cout << 4 << endl; 32 break; 33 case violet: 34 cout << 5 << endl; 35 break; 36 case indigo: 37 cout << 6 << endl; 38 break; 39 default: 40 cout << "输入有误，退出" << endl; 41 break; 42 } 43 cout << "跳出选择\n"; 44 } 45 cout << "跳出循环\n"; 46 return 0; 47 }
12. 带回车的字符串输入
1 #include <iostream> 2 #include <string> 3 #include <vector> 4 5 using namespace std; 6 7 int main() 8 { 9 string input{}; 10 int count{}; 11 12 cout << "请输入你需要的字符,用*结尾" << endl; 13 getline(cin, input, '*'); 14 count = static_cast<int>(input.length()); 15 16 cout << "字符个数为：" << input << endl; 17 18 }
