第二章 C++简单程序设计

1.引例：计算商品总价

#include <iostream>
using namespace std;
int main()
{
const double price1 = 25.5, price2 = 10.3, price3 = 12.5;
double total = 0;
int number1 = 0, number2 = 0, number3 = 0;
cout << "三种商品的价格为：" << price1 << ',' << price2 << ',' << price3 << '\n';
cout <<"请问每样买几件？" << endl;
cin >> number1 >> number2 >> number3;
total = number1 * price1 + number2 * price2 + number3 * price3;
cout << "应付款总额：" << total << endl;
return 0;
}

程序运行结果：

2.if 语句

用 if 语句实现选择
if(表达式）语句1 else 语句2 例：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;

§引例：输入一个年份，判断是否闰年

#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;
}

程序运行结果：

3.switch 语句——开关语句

switch ()

{

case 常量表达式1：语句1

case 常量表达式2：语句2

......

case 常量表达式n：语句n

default: 语句n+1

}

§引例：输入一个0~6 的整数，转换成星期输出

#include <iostream>
using namespace std;
int main()
{
int day;
cin >> day;
switch (day)
{
case 0:cout << "Sunday" << endl; break;
case 1:cout << "Monady" << endl; break;
case 2:cout << "Tuesday" << endl; break;
case 3:cout << "Wednesady" << 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 Sunday...Saturday" << endl; break;
}
return 0;
}