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Converting a 1 digit decimal number to ASCII representation

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• The simple case of converting ASCII representation -> 2's complement representation
  • Let's first study the following problem:

    Suppose we want to print a (binary) number that is between 0 and 9 (i.e.: a single digit decimal number). I.e.: we only want to print one of the following binary numbers: 00000000 00000001 00000010 00000011 00000100 00000101 00000110 00000111 00001000 00001001 These 2's complement codes represents the values zero, one, two, ..., nine Write a Java program that converts any of these 10 values into their corresponding ASCII character codes

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  • We must perform the following 10 conversions:

    Input Output 2's complement (int) code ASCII character code --------------------------- ------------------------------------- 00000000 (zero) --> 00110000(2) = 48(10) (character '0') 00000001 (one) --> 00110001(2) = 49(10) (character '1') 00000010 (two) --> 00110010(2) = 50(10) (character '2') 00000011 (three) --> 00110011(2) = 51(10) (character '3') 00000100 (four) --> 00110100(2) = 52(10) (character '4') 00000101 (five) --> 00110101(2) = 53(10) (character '5') 00000110 (six) --> 00110110(2) = 54(10) (character '6') 00000111 (seven) --> 00110111(2) = 55(10) (character '7') 00001000 (eight) --> 00111000(2) = 56(10) (character '8') 00001001 (nine) --> 00111001(2) = 57(10) (character '9')

    The output of the conversion can be accomplished by the following mapping operation (because the ASCII codes are consecutive):

    ASCII code = 2's complement code + 48

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  • Here is a Java program uses the above mapping function to convert an int (2's complement code) to a String:

    // File: /home/cs255001/demo/atoi/JavaOutput_2.java // // Converting a binary number between 0 and 9 to a String // public class JavaOutput_2 { public static void main(String[] args) throws Exception { int i; char[] c = new char[1]; // char array of size 1 // (because we only have 1 character) i = 4; // *** Change to any value between 0 and 9 c[0] = (char) (i + 48); // c is equal to ASCII code for the number ! /* --------------------------------------------- Make a string out of the character(s) ---------------------------------------------- */ String s = new String(c); System.out.println(">>> " + s); /* --------------------------------------------- Prove to students that s is a string ---------------------------------------------- */ s = s + " - hello, this is a string !"; System.out.println(">>> " + s); } }

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  • Example Program: (Demo above code)                                                

    How to run the program:

    Get a copy from: /home/cs255001/demo/atoi/JavaOutput_2.java To compile:   javac JavaOutput_2.java To run:          java JavaOutput_2

    You can change the statement i = 4; to any value between 0 and 9.

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  • Quiz:

    You can give i a value larger than 9, but you will get some strange. Try to figure out why for i = 10;, the program will print : (colon). Hint: look in the ASCII table...

    Answer:

    When i = 10, the program will print the character that corresponds to the ASCII code value 10 + 48 = 58 According to the ASCII table, the ASCII code 58 represents the character : That's why you see : printed by the program.