The operating system used is MS-DOS
MS-DOS : The MS-DOS is a single user, single process, single processor operating system. Due to the confinement of the device dependent code into one layer, the porting of MS-DOS has theoretically been reduced to writing of the BIOS code for the new hardware. At the command level it provides a hierarchical file system, input output redirection, pipes and filters. User written commands can be invoked in the same way as the standard system commands, giving the appearance as if the basic system functionality has been extended.
Being a single user system, it provides only file protection and access control. The disk space is allocated in terms of a cluster of consecutive sectors. The command language of MS-DOS has been designed to allow the user to interact directly with the operating system using a CRT terminal. The principal use of the command language is to initiate the execution of commands and programs. A user program can be executed under MS-DOS by simply typing the name of the executable file of the user program at the DOS command prompt.
The programming language used here is C programming
SYSTEM DESIGN
Process
The lexical analyzer is the first phase of a compiler. Its main task is to read the input characters and produce as output a sequence of tokens that the parser uses for syntax analysis. This interaction, summarized schematically in fig below.
Upon receiving a �get next token �command from the parser, the lexical analyzer reads the input characters until it can identify next token.
Sometimes , lexical analyzers are divided into a cascade of two phases, the first called �scanning�, and the second �lexical analysis�.
The scanner is responsible for doing simple tasks, while the lexical analyzer proper does the more complex operations.
The lexical analyzer which we have designed takes the input from a input file. It reads one character at a time from the input file, and continues to read until end of the file is reached. It recognizes the valid identifiers, keywords and specifies the token values of the keywords.
It also identifies the header files, #define statements, numbers, special characters, various relational and logical operators, ignores the white spaces and comments. It prints the output in a separate file specifying the line number .
BLOCK DIAGRAM
