do while

 语法：

do

{

 循环体;

}

While （条件）; //记住有分号

{

 

}

 

 

执行过程：

 

1）执行循环体 执行完循环休息转向2

2）判断条件是否成立，如果 条件为true.刚转向1 如果条件为False 则转向3

3）跳出循环体 结束

 

假如循环体一开始就不成立，对天while循环一次都不执行，对于do-while循环体会执行一次，所以do-while的循环体一般至少会执行一次，

while 先判断后执行

do while 先执行后判断

---

例1：

 

string answer;

do

{

Console.WriteLine("小兰表演一遍舞蹈!");

Console.WriteLine("老师你满意吗 （y / n）");  //循环体

answer=Console.ReadLine();

}while (answer!="y"); //循环条件

Console.WriteLine("跳得不错。回家吧");

Console.ReadKey();

---

 

 

例2  嵌入了一个 while循环  (来限定只能输入y n)

 

string answer;

do

{

Console.WriteLine("小兰表演一遍舞蹈!");

Console.WriteLine("老师你满意吗 （y / n）");

answer=Console.ReadLine();

while (answer!="y"&&answer!="n") //嵌入了一个while循环

{

Console.WriteLine("只能输入y或者n!");

answer = Console.ReadLine();

}

}while (answer!="y");

Console.WriteLine("跳得不错。回家吧");

Console.ReadKey();

---

int sum = 0;

int i = 1;

while (i<=100)

{

sum += i;

i++;

}

Console.WriteLine(sum);

Console.ReadKey();

 

---

 

int a = 1, b = 100;

int sum = 0;

int i =1 ;

while (i<=50)

{

sum =sum+(a+b); //如果此处改为sum=a+b  可以体会循环的真正用法  因为这样永远是a+b 而没有把每次相加后的结果累加起来.

a++;

b--;

i++;

}

Console.WriteLine("{0}", sum);

Console.ReadKey();

---

 

2种写法

string userName;

string passWord;

do

{

Console.WriteLine("请输入用户名");

userName = Console.ReadLine();

Console.WriteLine("请输入密码");

passWord = Console.ReadLine();

if (userName != "admin" || passWord != "888888")

{

Console.WriteLine("错误请重新输入");

}

} while (userName != "admin" || passWord != "888888");

Console.WriteLine("输入正确");

Console.ReadKey();

 

string userName;

string passWord;

bool flag = false;

do

{

flag = false;

Console.WriteLine("请输入用户名");

userName = Console.ReadLine();

Console.WriteLine("请输入密码");

passWord = Console.ReadLine();

if (userName != "admin" || passWord != "888888")

{

Console.WriteLine("错误请重新输入");

flag = true;

}

} while (flag);

Console.WriteLine("输入正确");

Console.ReadKey();

---

 

string stuName;

do

{

Console.WriteLine("请输入学生姓名");

stuName = Console.ReadLine();

} while (stuName != "q");

{

Console.WriteLine("程序结束");

}

Console.ReadKey();

---

 

 

int number;

bool flag = false;

do

{

try

{

Console.WriteLine("请输入一个数字");

number = Convert.ToInt32(Console.ReadLine());

Console.WriteLine("{0}的2倍是:{1}", number, number *2);

flag = true;

}

catch

{

flag = false;

}

 

}while (flag);

{

Console.WriteLine("程序结束");

}

Console.ReadKey();

---

 

 

 

 

int number;

string input;

Console.WriteLine("请输入一个数字。（q）结束");

input = Console.ReadLine();

while (input != "q")

{

number = Convert.ToInt32(input);

Console.WriteLine("{0}的双倍是:{1}",number,number*2);

Console.WriteLine("请输入一个数字。（q）结束");

input = Console.ReadLine();

}

Console.WriteLine("程序结束");

Console.ReadKey();

---

 

int max = 0;

string input = "";

int number = 0;

 

do

{

try

{

Console.WriteLine("请输入一个数");

input = Console.ReadLine();

number = Convert.ToInt32(input);

if (number > max)

{

max = number;

}

}

catch

{

if (input != "end")

{

Console.WriteLine("输入非法数字！程序结束");

input = "end";

}

}

} while (input != "end");

{

}

Console.WriteLine("最大值：{0}",max);

Console.ReadKey();

---

do

{

try

{

Console.WriteLine("请输入一个数");

input = Console.ReadLine();

number = Convert.ToInt32(input);

if (number > max)

{

max = number;

}

}

catch

{

if (input != "end")

{

Console.WriteLine("输入非法数字！程序结束");

input = "end";

}

}

} while (input != "end");

{

}

Console.WriteLine("最大值：{0}", max);

Console.ReadKey();