c++while loop

1.while loop

• Format:

while(循环条件){
    
    
循环体；
}

• In the loop, we control the number of loops by controlling variables.
  Three elements of loop:
  initial value of loop variable,
  judgment of loop variable,
  update of loop variable

eg1：

#include <iostream>
using namespace std;
int main()
{
    
    
    int i = 1;
    while(i <= 10)
    {
    
    
        cout <<"小人本住在苏州的城边..\t第"<<i<<"遍\n";
        i++;
    }
    return 0;
}

Output:

小人本住在苏州的城边..  第1遍
小人本住在苏州的城边..  第2遍
小人本住在苏州的城边..  第3遍
小人本住在苏州的城边..  第4遍
小人本住在苏州的城边..  第5遍
小人本住在苏州的城边..  第6遍
小人本住在苏州的城边..  第7遍
小人本住在苏州的城边..  第8遍
小人本住在苏州的城边..  第9遍
小人本住在苏州的城边..  第10遍

eg2：

#include <iostream>
using namespace std;
int main()
{
    
    
    //目的：使用循环计算1-100的和
    int num=1;//循环变量的初值
    int sum=0;
    while(num<=100) //循环变量的判断
    {
    
    
        sum+=num;
        num++;//循环变量的更新
    }
    cout<<sum<<endl;

    return 0;
}

eg3

#include <iostream>
#include <cstdlib>
using namespace std;
int main()
{
    
    
    //目的：输入密码，3次都输入错误退出登录
    int i=1;
    string password;

    while(i<=3)
    {
    
    
        cout<<"请输入密码："<<endl;
        cin>>password;
        if(password!="123456"&&i==3)
        {
    
    

            cout<<"3次密码输入错误，系统强制退出"<<endl;
            exit(0);//0是错误码

        }
        else if(password=="123456")
        {
    
    
            break;
        }
        i++;
    }

    cout<<"登陆成功！"<<endl;
    return 0;
}

Exercises:
1.

#include <iostream>
#include <cstdlib>
using namespace std;
int main()
{
    
    
    int k=2;
    int i=0;
    while(k=1)
    {
    
    
    k=k-1;
    cout<<"第"<<++i<<"次循环"<<endl;
    }
    return 0;
}

This is an infinite loop. Because k=1it is an assignment operation and the return value is 1, while(1) will be executed. It is an infinite loop.

2. Determine whether the statement output is:

    int n=0;
    while(n++<=2);
    cout<<n;

The answer is 4.
Analysis: n++<=2, so n=2 when n enters for the last time, and then n++ is executed, that is, n=3; don’t forget to make a
judgment when finally jumping out of the loop, and execute n++ again. <=2 statement, n=3 at this time, does not meet the condition, but the ++ statement still needs to be executed, that is, n=n+1=4.

example:

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
int main()
{
    
    
    //使用循环模拟拳皇对战
    int hp1=100;
    int hp2=100;

    int attack1=0;
    int attack2=0;

    int randNum;

    srand(time(NULL));//更新随机种子

    while(hp1>=0&&hp2>=0)
    {
    
    

        //玩家出招，可以采用随机数是奇数还是偶数决定谁先攻击
        randNum=rand();
        if(randNum % 2==1)
        {
    
    
            //随机产生5到15的随机数
            attack1=(int)(5 + 10 *rand()/(RAND_MAX+1));
            attack2=(int)(5 + 10 *rand()/(RAND_MAX+1));

            hp2-=attack1;
            hp1-=attack2;

        }
        else
        {
    
    
            attack2=(int)(5 + 10 *rand()/(RAND_MAX+1));
            attack1=(int)(5 + 10 *rand()/(RAND_MAX+1));

            hp1-=attack2;
            hp2-=attack1;
        }

    }

    cout<<"玩家1："<<hp1<<endl;
    cout<<"玩家2："<<hp2<<endl;


    return 0;
}