C program for Lexical Analyzer

Editorial Team — Mon, 29 Mar 2010 16:16:52 +0000

#include
#include
#include
#include
#include
#include
struct pgm
 {
   char line[20];
 } s[100];
void check(char s[])
 {
    cout<<"\n";
    if(!strcmpi(s,"If"))
     {
        cout<<"keyword:If";
        return;
     }
    if(!strcmpi(s,"Then"))
     {
       cout<<"keyword:Then";
       return;
     }
    if(!strcmpi(s,"Else"))
     {
       cout<<"keyword:else";
       return;
     }
    if(!strcmpi(s,"[END]"))
     {
       return;
      }
    cout<<"expression:"<The post C program for Lexical Analyzer first appeared on Student Projects.

Sudoku Solver using C++

Editorial Team — Thu, 20 Nov 2008 10:01:11 +0000

You have seen it in the news papers, you have seen it in the magazines or in the web sites, you might have sat hours ‘n hours to solve it. Yes, it is the king of all number puzzles, it is “SUDOKU”.

We bring to you the ultimate solution for all your struggles, The SUDOKU Solver.

As you know, now a days mathematical puzzle-SUDOKU is in boom all over the world. Sudoku is a 9X9 matrix with nine 3×3 sub-matrices, that we need to fill by entering the numbers from 1 through 9, without the repetition of the a number in the rows, columns or in the sub matrices.

Figure: 1- Sudoku Problem

We can get the Sudoku puzzle in ease by different means, as discussed. You might have struggled a lot to solve the same. To be true, even me too. Here I developed a fast and robust package, that solves the puzzles, that are not easy to solve by hands. It will solve the Sudoku entered in fraction of a milli-second and will display the solved result.

Figure: 2 – Sudoku Result

Click here to download the executable files

When the code executes, a blank Sudoku will be displayed with 9×9 red boxes. The user is needed to enter the numbers corresponding to the source puzzle (Figure 1). To enter this, user should use the arrow keys to cruse to the required box. The selected box will be highlighted with a blue boundary. You have to enter the number through the keyboard. Once you have done entering all the numbers in the puzzle just hit the ‘Enter’ key on the keyboard till you get the solved result (Figure 2). If the Sudoku cannot be solved by this program a message will be displayed telling that the given puzzle cannot be solved.

The post Sudoku Solver using C++ first appeared on Student Projects.

Lexical Analyzer

Editorial Team — Thu, 20 Nov 2008 07:37:32 +0000

Lexical analyzer converts stream of input characters into a stream of tokens. The different tokens that our lexical analyzer identifies are as follows:

KEYWORDS: int, char, float, double, if, for, while, else, switch, struct, printf, scanf, case, break, return, typedef, void

IDENTIFIERS: main, fopen, getch etc

NUMBERS: positive and negative integers, positive and negative floating point numbers.

OPERATORS: +, ++, -, –, ||, *, ?, /, >, >=, <, <=, =, ==, &, &&.

BRACKETS: [ ], { }, ( ).

STRINGS : Set of characters enclosed within the quotes

COMMENT LINES: Ignores single line, multi line comments

For tokenizing into identifiers and keywords we incorporate a symbol table which initially consists of predefined keywords. The tokens are read from an input file. If the encountered token is an identifier or a keyword the lexical analyzer will look up in the symbol table to check the existence of the respective token. If an entry does exist then we proceed to the next token. If not then that particular token along with the token value is written into the symbol table. The rest of the tokens are directly displayed by writing into an output file.

The output file will consist of all the tokens present in our input file along with their respective token values.

INTRODUCTION:

Lexical analysis involves scanning the program to be compiled and recognizing the tokens that make up the source statements Scanners or lexical analyzers are usually designed to recognize keywords , operators , and identifiers , as well as integers, floating point numbers , character strings , and other similar items that are written as part of the source program . The exact set of tokens to be recognized of course, depends upon the programming language being used to describe it.

A sequence of input characters that comprises a single token is called a lexeme. A lexical analyzer can insulate a parser from the lexeme representation of tokens. Following are the list of functions that lexical analyzers perform.

Removal of white space and comment :

Many languages allow “white space” to appear between tokens. Comments can likewise be ignored by the parser and translator , so they may also be treated as white space. If white space is eliminated by the lexical analyzer, the parser will never have to consider it.

Constants :

An integer constant is a sequence of digits, integer constants can be allowed by adding productions to the grammar for expressions, or by creating a token for such constants . The job of collecting digits into integers is generally given to a lexical analyzer because numbers can be treated as single units during translation. The lexical analyzer passes both the token and attribute to the parser.

Recognizing identifiers and keywords :

Languages use identifiers as names of variables, arrays and functions. A grammar for a language often treats an identifier as a token. Many languages use fixed character strings such as begin, end , if, and so on, as punctuation marks or to identify certain constructs. These character strings, called keywords, generally satisfy the rules for forming identifiers.

SYSTEM ANALYSIS:

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. a.

fig a. Process of lexical analyzer

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:

fig b. Block diagram of the project

The post Lexical Analyzer first appeared on Student Projects.

C codes | Student Projects

C program for Lexical Analyzer

Sudoku Solver using C++

Lexical Analyzer