Octal Fractions

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 6669		Accepted: 3641

Fractions in octal (base 8) notation can be expressed exactly in decimal notation. For example, 0.75 in octal is 0.953125 (7/8 + 5/64) in decimal. All octal numbers of n digits to the right of the octal point can be expressed in no more than 3n decimal digits to the right of the decimal point.

Write a program to convert octal numerals between 0 and 1, inclusive, into equivalent decimal numerals.

The input to your program will consist of octal numbers, one per line, to be converted. Each input number has the form 0.d1d2d3 ... dk, where the di are octal digits (0..7). There is no limit on k.

Your output will consist of a sequence of lines of the form

0.d1d2d3 ... dk [8] = 0.D1D2D3 ... Dm [10]
where the left side is the input (in octal), and the right hand side the decimal (base 10) equivalent. There must be no trailing zeros, i.e. Dm is not equal to 0.

0.75

0.0001

0.01234567

0.75 [8] = 0.953125 [10]

0.0001 [8] = 0.000244140625 [10]

0.01234567 [8] = 0.020408093929290771484375 [10]

import java.util.*;

import java.io.*;

import java.math.*;

import java.text.*;

public class Main {

    public static void main(String[] args){

        Scanner sc = new Scanner(new BufferedInputStream(System.in));   ///用BufferedInputStream据说能快点

        BigDecimal ans, t, tmp;

        while(sc.hasNext()){

            String st = sc.nextLine();     ///字符串输入

            t = BigDecimal.valueOf(1);

            ans = BigDecimal.valueOf(0);

            int i, sta = st.indexOf('.');//找到第一次出现'.'  的位置

            for(i = sta+1; i < st.length(); ++i){              ///获取字符串长度只能用length（）方法

                tmp = BigDecimal.valueOf(st.charAt(i) - '0');  //charAt（）获取当前位置的字符

                t = t.divide(new BigDecimal("8"));           //大数只能和大数进行运算，Int只能与Int String只能和String

                tmp = tmp.multiply(t);//乘

                ans = ans.add(tmp);//加

            }

        System.out.println(st + " [8] = " + ans +  " [10]"); ///也可用System.out.printf();

        }

    }

}