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Problem: printing integer numbers

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• Problem description: why can't you print an int number ?
  • Recall that:

    Internally (= inside a computer program), (signed) integer values are represented using the 2's complement code: Value Internal representation (in 32 bits) ------------ ---------------------------------------- ... ... neg three 11111111111111111111111111111101 neg two 11111111111111111111111111111110 neg one 11111111111111111111111111111111 zero 00000000000000000000000000000000 one 00000000000000000000000000000001 two 00000000000000000000000000000010 three 00000000000000000000000000000011 ... ... twelve 00000000000000000000000000001100 ... ... The 2's complement representation is very efficient to perform arithmetic calculations (See: click here )

    For example: the value twelve is represented by 00000000000000000000000000001100

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  • Numbers are printed to the terminal by sending ASCII codes to the terminal:

    For example, to print 12 the computer must send these ASCII codes to the terminal: 00110001 00110010

    Problem:

    An int representation of a number cannot be naively (= directly) send to the terminal to display the number

    Again, there is a disconnect between internal (2's complement) representation of a number and what a terminal needs to receive to display the number

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  • This disconnect is summarized in this figure:

    Internally (= inside a Java program, the number 12 is represented by the binary number 00000000000000000000000000001100 In order to print (= show) 12 on the terminal (so the user can see it), the computer can't send the binary number 00000000000000000000000000001100, but 00110001 00110010, whcih are the ASCII codes that represent the characters 1 and 2 <

    Therefore: we need to convert the input (2's complement) representation to the ASCII representation

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  • The Java class Integer has provide the conversion method toString( ) to Java programmers to do the conversion.

    You may not have use this method in CS170/CS171, because the conversion also take place in the println( ) method.

    Here's an example how you can convert an int variable into a string:

    int i = 123; String s; s = Integer.toString(i); // Convert i to String representation

    Again, in CS255, we will reveal the secret inside the toString( ) method so you will understand the computer operation better.

    Also, unlike the Boolean example, the conversion from 2's complement representation of numbers to ASCII representation of numbers is more complex and will take more than 1 webpage to explain....