Program to implement Lexical Analyzer

 # include <iostream.h>
 # include <fstream.h>
 # include <string.h>
 # include <stdlib.h>
 # include <stdio.h>
 # include <conio.h>
 # include <ctype.h>


 //--------------------------  Global Variables  -------------------------//


 const int iRows = 34;
 const int iCols = 15;

 int iTT[iRows][iCols] = {0};


 //------------------------  Function Definitions  -----------------------//


 //------------------------  loadTransitionTable( )  ---------------------//

 void loadTransitionTable( )
 {
    fstream File(\"tt.txt\", ios::in|ios::nocreate);

    if (!File)
    {
       cout << \"\\n Unable to open the input file.\" << endl;
       cout << \"\\n Press any key to exit.\";

       getch( );
       exit(0);
    }

    char sInput[100]={NULL};

    for (int i = 0; i < iRows; i ++)
    {
       strset(sInput, NULL);

       File.getline(sInput, 80);

       char *sPtr=NULL;

       sPtr = strtok(sInput, \" \");

       iTT[i][0] = atoi(sPtr);

       for(int j = 1; j < iCols; j ++)
       {
      sPtr=strtok(NULL, \" \");

      iTT[i][j] = atoi(sPtr);
       }
    }

    File.close( );
 }

 //---------------------------  getNextState( )  -------------------------//

 int getNextState(int iState, char cChar)
 {
    if (isalpha(cChar))
       return iTT[iState][1];

    else if (isdigit(cChar))
       return iTT[iState][2];

    else if (cChar == \'.\')
       return iTT[iState][3];

    else if (cChar == \'\"\')
       return iTT[iState][4];

    else if (cChar == \'_\')
       return iTT[iState][6];

    else if (cChar == \'+\')
       return iTT[iState][7];

    else if (cChar == \'=\')
       return iTT[iState][8];

    else if (cChar == \'-\')
       return iTT[iState][9];

    else if (cChar == \'%\')
       return iTT[iState][10];

    else if (cChar == \'!\')
       return iTT[iState][11];

    else if (cChar == \'>\')
       return iTT[iState][12];

    else if (cChar == \'<\')
       return iTT[iState][13];

    else if (cChar == \'/\')
       return iTT[iState][14];

    return iTT[iState][0];
 }

 //----------------------------  isKeyword( )  ----------------------------//

 int isKeyword(char* sToken)
 {
    if (strlen(sToken) > 16 || strlen(sToken) == 0)
       return 0;

    char sKeywords[64][20] = {
                   \"asm\",\"auto\",\"bool\",\"break\",\"case\",\"catch\",
                   \"char\",\"class\",\"const\",\"const_cast\",
                   \"continue\",\"default\",\"delete\",\"do\",\"double\",
                   \"dynamic_cast\",\"else\",\"enum\",\"explicit\",
                   \"export\",\"extern\",\"false\",\"float\",\"for\",
                   \"friend\",\"goto\",\"if\",\"inline\",\"int\",\"long\",
                   \"main\",\"mutable\",\"namespace\",\"new\",
                   \"operator\",\"private\",\"protected\",\"public\",
                   \"register\",\"reinterpret_cast\",\"return\",
                   \"short\",\"signed\",\"sizeof\",\"static\",
                   \"static_cast\",\"struct\",\"switch\",\"template\",
                   \"this\",\"throw\",\"true\",\"try\",\"typedef\",
                   \"typeid\",\"typename\",\"union\",\"unsigned\",\"using\",
                   \"virtual\",\"void\",\"volatile\",\"wchar_t\",\"while\"
                 };

    for(int iCount = 0; iCount < 64; iCount ++)
    {
       if (strcmpi(sKeywords[iCount], sToken) == 0)
      return 1;
    }

    return 0;
 }


 //-------------------------------  main( )  -----------------------------//


 int main( )
 {
    clrscr( );

    loadTransitionTable( );

    fstream File(\"input.txt\", ios::in|ios::nocreate);

    if (!File)
    {
       cout<<\"\\n Unable to open the input file.\"<<endl;
       cout<<\"\\n Press any key to exit.\";

       getch( );
       exit(0);
    }

    char sToken[255] = {NULL};
    int iTokenIndex = 0;

    char cChar = NULL;
    int iState = 0;
    int iFlag = 0;

    char cTemp = File.get( );

    do
    {
       Start:

       if (iFlag == 0)
       {
      cChar = cTemp;
      cTemp = File.get( );
       }

       else
      iFlag = 0;

       if (cChar == \'/\' && cTemp == \'/\')
       {
      while(File.get( ) != \'\\n\')
      {
         if (File.eof( ))
        goto End;
      }

      cout<<\'\\r\';

      cTemp = File.get( );

      goto Start;
       }

       if (cChar == \'/\' && cTemp == \'*\')
       {
      cTemp = File.get( );

      do
      {
         cChar = cTemp;
         cTemp = File.get( );

         if (File.eof( ))
        goto End;
      }
      while(cChar != \'*\' && cTemp != \'/\');

      cout<<\'\\r\';

      cTemp = File.get( );

      goto Start;
       }

       iState = getNextState(iState, cChar);

       switch (iState)
       {
      case  0 :  cout << cChar;

             iState = 0;
             iTokenIndex = 0;

             strset(sToken, NULL);

             break;

      case  1 :
      case  3 :
      case  5 :
      case  7 :
      case 10 :
      case 14 :
      case 18 :
      case 25 :
      case 26 :  sToken[iTokenIndex] = cChar;
             iTokenIndex ++;

             break;

      case  2 :  if (isKeyword(sToken))
            cout << sToken;

             else
            cout << \"<ID>\";

             iState = 0;
             iTokenIndex = 0;
             iFlag = 1;

             strset(sToken, NULL);

             break;

      case  4 :  cout << \"<INT>\";

             iState = 0;
             iTokenIndex = 0;
             iFlag = 1;

             strset(sToken, NULL);

             break;

      case  6 :  cout << \"<FLOAT>\";

             iState = 0;
             iTokenIndex = 0;
             iFlag = 1;

             strset(sToken, NULL);

             break;

      case  8 :  cout << \"<STR>\";

             iState = 0;
             iTokenIndex = 0;

             strset(sToken, NULL);

             break;

      case  9 :
      case 11 :
      case 12 :
      case 13 :
      case 15 :
      case 16 :
      case 17 :
      case 19 :
      case 20 :
      case 21 :
      case 22 :
      case 23 :
      case 24 :
      case 27 :
      case 28 :  cout << \"<OPR>\";

             if (cChar != \'+\' && cChar != \'-\' && cChar != \'/\'
                && cChar != \'>\' && cChar != \'<\' && cChar != \'=\')
            iFlag = 1;

             iState = 0;
             iTokenIndex = 0;

             strset(sToken, NULL);

             break;

      case 30 :
      case 33 :  iState = 0;
             iTokenIndex = 0;

             strset(sToken, NULL);

             break;
       }
    }
    while(!File.eof( ));

    End:

    getch( );
    return 0;
 }


 //------------------------------  THE END  ------------------------------//