c++作业3：项目2到项目四

项目二：本月有几天
#include <iostream.h>
void main()
{
int year, month, days;
cout << "请输入年、月"  ;
switch (month)
{
case 1:cout << "days=31"  ; break;
case 3:cout << "days=31"  ; break;
case 5:cout << "days=31"  ; break;
case 7:cout << "days=31"  ; break;
case 8:cout << "days=31"  ; break;
case 10:cout << "days=31"  ; break;
case 12:cout << "days=31"  ; break;
case 4:cout << "days=30"  ; break;
case 6:cout << "days=30" ; break;
case 9:cout << "days=30"  ; break;
case 11:cout << "days=30"  ; break;
case 2:
{if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0)
cout << "days=29"  ;
else
cout << "days=28"  ; }
break;
}
cout << year << "年" << month << "月共有" << days << "天" << endl;

}

/*项目三：定期存款利息*/
#include <iostream.h>
#include <math>
void main()
{
int principle;
double interest,PPI;
cout << "欢迎使用利息计算器！" ;
cout << "请输入存款金额（本金）" ;
cin >> principle >> ;
cout << "请选择存款期限\n1、三个月\n2、六个月\n3、一年\n4、二年\n5、三年\n6、五年\n"  ;
switch (date)
{
case'1':interest = 0.0031*principle; break;
case'2':interest = 0.0033*principle; break;
case'3':interest = 0.0035*principle; break;
case'4':interest = 0.0044*principle; break;
case'5':interest = 0.0050*principle; break;
case'6':interest = 0.0055*principle; break;
default:cout << "error\n"; break;
}
PPI = interest + principle;
cout << "到期利息为" << interest << \n << "本息合计共" << \n << PPI << "元"  ;
}

/*项目四*/
#include <iostream.h>
#include <math.h>
int main()
{
float x, y;
cout << "请输入一个实数x" ;
cin x;
extent == (x <10) + ( x<6) + ( x < 2) ;
switch (extent)
{
case 3:y = x; break;
case 2:y = x*x + 1; break;
case 1:y = sqrt(x + 1); break;
case 0:y = 1 / (x + 1); break;
default:cout << "error\n" ;
}
cout << "y=" << y ;
}