We just learned that key board/terminal uses the ASCII code to represent the input/output data

Specifically:

The number 12 is represented by the ASCII codes: 00110001 00110010 (binary)

In 2'c complement code, the value 12 is represented as: 00001100 (in 8 bits) 0000000000001100 (in 16 bits) 00000000000000000000000000001100 (in 32 bits)

The computer uses many different representations (= encoding methods) for the same "information" The encoding method (= representation method) the tha computer will use to represent the data will used depend on the purpose (= context) Example: The computer uses 2's complement representation if it needs to perform computation on the data The computer uses ASCII representation if it needs to input/output the data from/to a key board/terminal

Example: integer input

Suppose the program needs an integer value for input in some computation Since the integer value is used for computation, we want to use the 2's complement representation for the integer value However, the key board device uses the ASCII representation for the input data That means: when the user types in: 12 The computer will receive these ASCII codes as input: 00110001 00110010 But in order to perform computation, the number 12 must be represented by 00000000000000000000000000001100 !! Therefore: We need to convert the ASCII input representation (emitted by the keyboard) to the corresponing 2's complement representation BTW: that's is why you need to use the following construct to read in numbers in a Java program: String s = in.next( ); // Read input - it's always in ASCII code int i = Integer.parseInt( s ); // Convert ASCII repr to 2's compl repr (The method in.nextInt( ) combines the in.next( ) and the Integer.parseInt( ) for your convenience.)

ASCII representation <--> Boolean representation (This is a very simple conversion and I use it to introduce the next harder one) ASCII representation <--> int 2's complement representation