[CrackCode] 5.2 Print the binary representation

Given a (decimal - e g 3.72) number that is passed in as a string, print the binary rep-resentation If the number can not be represented accurately in binary, print “ERROR” 

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Analysis:

This is a typical example of how to transform a decimal number to binary number.  Basic idea is to divide the decimal number into 2 parts, i.e., the int part (e.g. 3), and the decimal part (e.g. 0.72).

For int part, similar approach of extracting numbers from int:

1. use %2 to get each digit from lowest bit to highest bit.

2. int right shift 1 position (=>>1).

3. construct the binary number (always add to the higher position of the current binary number)

Please refer to the code below for the process above.

For decimal part, use *2 approach.  For example:

int n = 0.75

n*2 = 1.5

Therefore, the first digit of binary number after '.' is 1 (i.e. 0.1).  After constructed the first digit, n= n*2-1 (remaining number would actually be *(2^2) before calculating the next digit)

When the remaining number ==1, the decimal number has been successfully transformed to binary number.  Otherwise, the decimal number could not be transform to binary number.

public class Answer {public static String printBinary(String str){int intPart = Integer.parseInt(str.substring(0,str.indexOf('.')));double decPart = Double.parseDouble(str.substring(str.indexOf('.')));// transform int part to binaryString int_string = "";while(intPart>0){int r = intPart%2;intPart>>=1;int_string = r+int_string;}// transform dec part to binaryStringBuffer dec_string=new StringBuffer();while(decPart>0){if(dec_string.length()>32) return "ERROR!";if(decPart == 1){// exitdec_string.append((int)decPart);break;}double r = decPart*2;if(r>=1){dec_string.append("1");decPart = r-1;}else{dec_string.append("0");decPart = r;}}return (int_string + "." + dec_string);}public static void main(String[] args) {String n = "19.25";String bs = printBinary(n);System.out.println(bs);}