JAVA基础学习（4）之循环控制

4循环控制

• 4.1 for循环
  • 4.1.1 for循环
    • 固定次数for循环
    • 先执行一次do-while循环
    • 其他while循环

    • Scanner in = new Scanner(System.in);//计算阶乘
              int n = in.nextInt();
              int factor = 1;
              ;
              for (int i = 1; i <= n; i++)
              {
      //            factor=i*factor;
                  factor *= factor;
              }
              System.out.println(n + "的阶乘值为：" + factor);

  • 4.1.2 复合赋值
    • a*=6 -> a=a*6
    • a/=b+6 -> a=a/(b*6)
    • i=i+1 ->i i++

    • Scanner in = new Scanner(System.in);//判断素数
              int n = in.nextInt();
              int flag = 0;
              for (int i = 2; i < n; i++)
              {
                  if (n % i == 0)
                  {
                      flag = 1;
                      break;
                  }
              }
              if (flag == 1)
              {
                  System.out.println(n + "不是素数!");
              } else
              {
                  System.out.println(n + "是素数！");
              }

• 4.2循环控制
  • 4.2.1循环控制
    • 素数判断

    • for (int n = 2; n < 100; n++)//输出100以内的素数
              {
                  int flag = 1;
                  for (int i = 2; i < n; i++)
                  {
                      if (n % i == 0)
                      {
                          flag = 0;
                          break;
                      }
                  }
                  if (flag == 1)
                  {
                      System.out.print(n + " ");
                  }
              }

    • break跳出循环
    • continue跳出循环这一轮的语句进入下一轮
  • 4.2.2多重循环
    • lable：
    • 标号标示循环，break lable或 continue lable 可以跳出

    •                 int count = 1;//输出前59个素数
              int n = 2;
              while (count <= 50)
              {
                  int flag = 1;
                  for (int i = 2; i < n; i++)
                  {
                      if (n % i == 0)
                      {
                          flag = 0;
                          break;
                      }
                  }
                  if (flag == 1)
                  {
                      System.out.println("第" + count + "个素数：" + n);
                      count++;
                  }
                  n++;
              }                

  • 4.2.3逻辑类型
    • 按照优先级排列
    • ！
    • &&
    • ||
    • 　

      Scanner in = new Scanner(System.in);//凑硬币
              int amount = in.nextInt();
              OUT: for (int one = 0; one <= amount; one++)
              {
                  for (int five = 0; five <= amount / 5; five++)
                  {
                      for (int ten = 0; ten <= amount / 10; ten++)
                      {
                          for (int twenty = 0; twenty <= amount / 20; twenty++)
                          {
                              if ((one + 5 * five + 10 * ten + 20 * twenty) == amount)
                              {
                                  System.out.println(one + "张1元，" + five + "张5元，" + ten + "张10元，" + twenty + "张20元");
                                  break OUT;
                              }
                          }
                      }
                  }
              }

    • 
• 4.3循环的例子
  • 4.3.1求和
    • 　　

      Scanner in = new Scanner(System.in);// f=1-1/2+1/3...求和
              int n = in.nextInt();
              double sum=0;
              int sign=1;
              for (int i = 1; i <= n; i++,sign=-sign)
              {
                  sum+=sign*1.0/i;
              }
              System.out.println("和为："+sum);
              System.out.print("和为：");
              System.out.printf("%.2f",sum);

  • 4.3.2最大公约数
    • 　　

      Scanner in=new Scanner(System.in);//求最大公约数
              int a=in.nextInt();
              int b=in.nextInt();
              int gcd=1;
      //        for(int i=2;i<=a&&i<=b;i++)
              for (int i = 2; i <= (a<b?a:b); i++)
              {
                  if((a%i==0)&&(b%i==0))
                  {
                      gcd=i;
                  }
              }
              System.out.println(a+"和"+b+"最大公约数为:"+gcd);

    • Scanner in=new Scanner(System.in);//辗转相除法求最大公约数
              System.out.println("请输入a和b：");
              int a=in.nextInt();
              int b=in.nextInt();
              
              while (b!=0)
              {
                  int r=a%b;
                  System.out.println(a+" "+b+" "+r);
                  a=b;
                  b=r;
              }
              System.out.println("最大的公约数为："+a);