随机产生50个100以内的正整数放入数组中，输出这50个整数（每行10个），再输入一个整数i，删除数组中第i个整数，然后输出删除第i个整数后的数组。

    public void printArr(int a[], int len, int line) {
        System.out.println("数组:");
        for(int i = 0; i < len; ) {
            System.out.print(a[i++] + "\t");
            if(i % line == 0) System.out.println();
        }
    }
    public void arrOp() {
        int i, a[], len = 50, MAX = 100;
        a = new int[len];
        for(i = 0; i < len; i++) {
            //Math.random()  -> Returns a double value with a positive sign, greater than or equal to 0.0 and less than 1.0.
            a[i] =  (int)(Math.random() * MAX);// 0<= a[i] < MAX;
        }
        printArr(a, len, 10);
        boolean valid = true;
        while(true) {
            //format();   %[argument_index$][flags][width][.precision]conversion
            System.out.print(String.format("\n输入一个大于等于 %d 小于 %d的数,  \'q\'结束: " , 0, len));
            int c = 0, index = 0;
            try {
                while(c !=13) { //回车13 换行10
                    c =  System.in.read(); //从系统输入流读取一个字符, 这个函数错误时会抛出异常
                    if('q' == c || 'Q' == c) {return ;}//碰上字母Q, 退出
                    else if( '0' <= c && '9'>= c) {//是数字
                        index = c - '0' + index * 10; //持续输入数字
                        if(index >= len) {//预期输入在0~len之间, 不包括len
                             valid = false; System.out.println("输入太大"); break;
                        }
                    }
                    else if(13 == c) {//回画,  获取全部数字
                        break;
                    }
                    else {//不是数字且不是回车
                        System.out.println("input error"); valid = false; break;
                    }
                }
                if(valid) {//输入合法, 删除指定位置的数字, 即把后面的数字往前移一格
                    for(i = index; i < len - 1; i ++) a[i] = a[i+1];
                    len--;
                    printArr(a, len, 10);
                }
                valid = true; index = 0;
                //System.in.skip(System.in.available());//忽略多余的输入, 按一下回车键, 会产生13 10两个字符
            } catch (IOException e) {
                e.printStackTrace();//打印异常
                break; //退出循环
            }
        }
    }