第2章 C++的简单程序设计（一）
C++语言概述
命名空间
避免命名冲突：
std是C++标准库的命名空间（ namespace）名
using namespace std表示打开std命名空间
#include <iostream> //编译预处理命令
using namespace std; //避免命名冲突
int main(){
cout<< "Hello!" << endl;
return 0;
}
基本数据类型、常量、变量
//初始化
int a=0;
int a(0);
int a={0};
int a{0};
//常量
const float PI=3.1415926;
程序举例
读入并显示数据
int main()
{
//读入并显示整数
const double pi(3.14); //符号常量
int radius(0); //变量初始化
cout << "The initial value of radius is " << radius << "\n";
cout << "Please enter the radius!\n";
cin >> radius;
cout << "The radius is " << radius << "\n";
cout << "Pi is " << pi << "\n";
cout << "Please enter a different radius!\n";
cin >> radius;
cout << "Now the radius is " << radius;
return 0;
}
运算与表达式
sizeof, 位运算
sizeof运算
语法形式： sizeof (类型名) 或 sizeof 表达式
结果值：
“类型名”所指定的类型，或“表达式”的结果类型所占的字节数。
例：
sizeof(short)
sizeof x
位运算
按位与：某些位置0
按位或：某些位置1
按位异或：相同为0，不同为1。某些位翻转
数据的输入和输出
cout<<表达式1<<表达式2
int a,b;
cin>>a>>b;
选择结构
if 语句
if (x>y) cout<<x;
if (x>y) cout <<x;
else cout<<y;
if (表达式1) 语句1;
else if (表达式2) 语句2;
else if (表达式3) 语句3;
...
else 语句n;
//输入一个年份，判断是否是闰年
#include <iostream>
using namespace std;
int main()
{
int year;
bool isLeapYear;
cout<<"enter the year:";
cin>>year;
isLeapYear= ((year%4==0 && year%100!=0)||(year%400=0));
if (isLeapYear)
cout<<year<<"is a leap year"<<endl;
else
cout<<year<<"is not a leap year"<<endl;
return 0;
}
//输入两个整数，比较两个整数的大小
#include <iostream>
using namespace std;
int main()
{
int x, y;
cout << "enter x and y:";
cin >> x >> y;
if (x > y)
cout << "x>y" << endl;
else if (x == y)
cout << "x=y" << endl;
else
cout << "x<y";
return 0;
}
switch语句
//输入一个0-6的整数，并且转换为星期输出
#include <iostream>
using namespace std;
int main()
{
int number;
cout << "Enter a number (0-6):";
cin >> number;
switch(number){
case 0: cout << "Sunday" << endl; break;
case 1: cout << "Monday" << endl; break;
case 2:cout << "Tuesday" << endl; break;
case 3:cout << "Wednesday" << endl; break;
case 4: cout << "Thursday" << endl; break;
case 5:cout << "Friday" << endl; break;
case 6:cout << "Saturday" << endl; break;
default: cout << "Day out of range." << endl; break;
}
return 0;
}
循环结构
while循环
//求自然数1-10的和
#include <iostream>
#using namespace std;
int main()
{
int i(1),sum(0);
while (i <= 10)
{
sum += i;
i += 1;
}
cout << sum << endl;
return 0;
}
do while
//输入一个数，将各位数字翻转后输出
#include <iostream>
using namespace std;
int main()
{
cout << "enter a number:" << endl;
int number;
cin >> number;
do
{
cout << number % 10;
number /= 10;
} while (number != 0);
return 0;
}
//输出0-10的和
#include <iostream>
using namespace std;
int main()
{
int i = 1, sum = 0;
do {
sum += i;
i += 1;
} while (i <= 10);
cout << sum << endl;
return 0;
}
for 语句
//输入一个整数，求出他所有的因子
#include <iostream>
using namespace std;
int main()
{
int number;
cout << "enter a postive number:";
cin >> number;
cout << "number " << number << " factors:";
for (int i = 1; i <= number; i++) {
if (number%i == 0) {
cout << i<<" ";
}
}
return 0;
}
嵌套的控制结构、其他控制语句
//输入一系列整数，统计出正整数个数i和负整数个数j，读入0则结束
using namespace std;
int main()
{
int pos = 0, neg = 0, n;
cout << "enter some integers (enter 0 to quit):";
cin >> n;
while (n != 0) {
if (n > 0) pos += 1;
else if (n < 0) neg += 1;
cin >> n;
}
cout << pos << " postive integers" << endl;
cout << neg << " negative integers" << endl;
return 0;
}
其他控制语句
自定义类型
类型别名：为已有类型另外命名
枚举类型
//设某次体育比赛的结果有4种可能：胜（WIN），负（LOSE），平局（TIE），比赛取消（CANCEL），编写程序顺序输出这四种情况
using namespace std;
enum GameResult {WIN,LOSE,TIE,CANCEL};
int main()
{
GameResult result;
enum GameResult omit = CANCEL;
for (int count = WIN; count <= CANCEL; count++) {
result = GameResult(count);
if (result == omit) cout << "The game was cancelled." << endl;
else
{
cout << "The game was played" ;
if (result == WIN) cout << " and we won!";
if (result == LOSE) cout << " and we lost!";
cout << endl;
}
}
return 0;
}
auto类型与decltype类型
实验
面积
#include <iostream>
using namespace std;
const float PI = 3.1416;
int main()
{
cout << "please select a type (1-circle, 2-rectangle 3-square):";
int type;
cin >> type;
switch (type) {
case 1:
cout << "please enter r:";
float r;
cin >> r;
cout << "the area is " << PI * r*r << endl;
break;
case 2:
cout << "please enter the width and height:";
float wid, hei;
cin >> wid >> hei;
cout << "the area is " << wid * hei << endl;
break;
case 3:
cout << "please enter the length:";
float len;
cin >> len;
cout << "the area is " << len * len << endl;
break;
defalt:
cout << "sorry. please enter a correct type." << endl;
}
return 0;
}
时间
声明一个表示时间的结构体，可以精确表示年、月、日、小时、分、秒，提示用户输入年、月、日、小时、分、秒，然后完整地显示出来。
#include <iostream>
using namespace std;
const float PI = 3.1416;
struct myTimeStruct
{
unsigned int year;
unsigned int month;
unsigned int day;
unsigned int hour;
unsigned int min;
unsigned int sec;
};
int main()
{
myTimeStruct myTime;
cout << "enter the year:";
cin >> myTime.year;
cout << "enter the month:";
cin >> myTime.month;
cout << "enter the day:";
cin >> myTime.day;
cout << "enter the hour:";
cin >> myTime.hour;
cout << "enter the min:";
cin >> myTime.min;
cout << "enter the sec:";
cin >> myTime.sec;
cout << "the time is set to "
<< myTime.year << "/"
<< myTime.month << "/"
<< myTime.day << " "
<< myTime.hour << ":"
<< myTime.min << ":"
<< myTime.sec << endl;
return 0;
}
作业题
#include <iostream>
using namespace std;
int main()
{
int n;
cin >> n;
int max, min;
int num,sum=0;
for (int i = 1; i <= n; i++) {
cin >> num;
sum += num;
if (i == 1) {
max = num;
min = num;
}
else {
if (num > max) max = num;
if (num < min) min = num;
}
}
cout << sum << " " << min << " " << max << endl;
}
#include <iostream>
using namespace std;
int main()
{
int n;
cin >> n;
int space, symbol;
for (int i = 1; i <= n; i++) {
symbol = 2 * i - 1; //number of symbols
space = (2 * n - 1 - symbol) / 2; //number of symbols
for (int j = 1; j <= space; j++)
cout << " ";
for (int j = 1; j <= symbol; j++)
cout << "*";
for (int j = 1; j <= space; j++)
cout << " ";
cout << endl;
}
for (int i = n - 1; i >= 1; i--) {
symbol = 2 * i - 1; //number of symbols
space = (2 * n - 1 - symbol) / 2; //number of symbols
for (int j = 1; j <= space; j++)
cout << " ";
for (int j = 1; j <= symbol; j++)
cout << "*";
for (int j = 1; j <= space; j++)
cout << " ";
cout << endl;
}
return 0;
}