Decimal Places

Why do you want to do this? A concept like "the number of decimal

places" seems to relate more naturally to the String form in which a

number is presented, rather than to a double, say. Often people decide

in advance how many decimal places they want (or how many make

sense) in the string forms of numbers, and round the numbers

accordingly.

You could try something like this:import java.io.BufferedReader;

import java.io.InputStreamReader;

public class DP {

public static void main(String[] args) throws Exception {

BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

double d = Double.parseDouble(in.readLine());

System.out.printf("dp=%d %f%n", getDP(d), d);

}

/**

* Returns how many times a number must be multiplied by 10 before

* the decimal bit compares equal to zero.

*/

private static int getDP(double d) {

double num = d - Math.floor(d);

//System.out.println("num="+num);

int ret = 0;

while(num != 0) {

ret++;

num *= 10;

num = num - Math.floor(num);

//System.out.println("num="+num);

}

return ret;

}

}

It "works" for the two examples you give. But it gives results that

can be unexpected (unless you expect them). For instance 0.99999

must be multiplied by 10 49 times before the decimal part becomes

zero.

The "number of decimal places" is not obvious for computer numbers

that are necessarily imprecise. In mathematics centuries of thought

finally managed to establish that pi and e don't have a number of

decimal places (they go on for ever). Mathematicians still have no

clue about the number pi+e.

pbrockway2a at 2007-7-14 1:10:11 >