A C Program on Lexical Analysis

#include

#include

#include

#include

#define MAX 30

 

 

void main()

{

char str[MAX];

int state=0;

int i=0, j, startid=0, endid, startcon, endcon;

 

 

clrscr();

 

 

for(j=0; j') state=21;   

 //relational '>' or '>='

 

 else if(str[i]=='=') state=23;   

 //relational '==' or assignment '='

 

 else if(isdigit(str[i])) 

 { 

state=25; startcon=i; 

 }

//constant

 

 else if(str[i]=='(') state=26;   

 //special characters '('

 

 else if(str[i]==')') state=27;   

 //special characters ')'

 

 else if(str[i]==';') state=28;   

 //special characters ';'

 

 else if(str[i]=='+') state=29;   

 //operator '+'

 

 else if(str[i]=='-') state=30;   

 //operator '-'

 

 break;

 

 

//States for 'if'

case 1: if(str[i]=='f') state=2;

 else { state=17; startid=i-1; i--; }

 break;

case 2: if(str[i]=='(' || str[i]==NULL)

 {

 printf("if : Keyword");

 state=0;

 i--;

 }

 else { state=17; startid=i-2; i--; }

 break;

 

 

//States for 'while'

case 3: if(str[i]=='h') state=4;

 else { state=17; startid=i-1; i--; }

 break;

case 4: if(str[i]=='i') state=5;

 else { state=17; startid=i-2; i--; }

 break;

case 5: if(str[i]=='l') state=6;

 else { state=17; startid=i-3; i--; }

 break;

case 6: if(str[i]=='e') state=7;

 else { state=17; startid=i-4; i--; }

 break;

case 7: if(str[i]=='(' || str[i]==NULL)

 {

 printf("while : Keyword");

 state=0;

 i--;

 }

 else { state=17; startid=i-5; i--; }

 break;

 

 

//States for 'do'

case 8: if(str[i]=='o') state=9;

 else { state=17; startid=i-1; i--; }

 break;

case 9: if(str[i]=='{' || str[i]==' ' || str[i]==NULL || str[i]=='(')

 {

 printf("do : Keyword");

 state=0;

 i--;

 }

 break;

 

 

//States for 'else'

case 10: if(str[i]=='l') state=11;

else { state=17; startid=i-1; i--; }

break;

case 11: if(str[i]=='s') state=12;

else { state=17; startid=i-2; i--; }

break;

case 12: if(str[i]=='e') state=13;

else { state=17; startid=i-3; i--; }

break;

case 13: if(str[i]=='{' || str[i]==NULL)

{

printf("else : Keyword");

state=0;

i--;

}

else { state=17; startid=i-4; i--; }

break;

 

 

//States for 'for'

case 14: if(str[i]=='o') state=15;

else { state=17; startid=i-1; i--; }

break;

case 15: if(str[i]=='r') state=16;

else { state=17; startid=i-2; i--; }

break;

case 16: if(str[i]=='(' || str[i]==NULL)

{

printf("for : Keyword");

state=0;

i--;

}

else { state=17; startid=i-3; i--; }

break;

 

 

//States for identifiers

case 17: 

 

if(isalnum(str[i]) || str[i]=='_') 

{ 

state=18; i++; 

}

else if(str[i]==NULL||str[i]=='<'||str[i]=='>'||str[i]=='('||str[i]==')'||str[i]==';'||str[i]=='='||str[i]=='+'||str[i]=='-') state=18;

i--;

break;

 

 

case 18: 

 

if(str[i]==NULL || str[i]=='<' || str[i]=='>' || str[i]=='(' || str[i]==')' || str[i]==';' || str[i]=='=' || str[i]=='+' ||str[i]=='-')

{

endid=i-1;

printf("");

for(j=startid; j<=endid; j++)

printf("%c", str[j]);

printf(" : Identifier");

state=0;

i--;

}

break;

 

 

//States for relational operator '<' & '<='

case 19: if(str[i]=='=') state=20;

else if(isalnum(str[i]) || str[i]=='_')

{

printf("< : Relational operator");

i--;

state=0;

}

break;

case 20: if(isalnum(str[i]) || str[i]=='_')

{

printf("<= : Relational operator");

i--;

state=0;

}

break;

 

 

//States for relational operator '>' & '>='

case 21: if(str[i]=='=') state=22;

else if(isalnum(str[i]) || str[i]=='_')

{

printf("> : Relational operator");

i--;

state=0;

}

break;

case 22: if(isalnum(str[i]) || str[i]=='_')

{

printf(">= : Relational operator");

i--;

state=0;

}

break;

 

 

//States for relational operator '==' & assignment operator '='

case 23: if(str[i]=='=') state=24;

else

{

printf("= : Assignment operator");

i--;

state=0;

}

break;

case 24: if(isalnum(str[i]))

{

printf("== : Relational operator");

state=0;

i--;

}

break;

 

 

//States for constants

case 25: if(isalpha(str[i]))

{

printf("*** ERROR ***");

puts(str);

for(j=0; j' || str[i]==NULL || str[i]==';' || str[i]=='=')

{

endcon=i-1;

printf("");

for(j=startcon; j<=endcon; j++)

printf("%c", str[j]);

printf(" : Constant");

state=0;

i--;

}

break;

 

 

//State for special character '('

case 26: printf("( : Special character");

startid=i;

state=0;

i--;

break;

 

 

//State for special character ')'

case 27: printf(") : Special character");

state=0;

i--;

break;

 

 

//State for special character ';'

case 28: printf("; : Special character");

state=0;

i--;

break;

 

 

//State for operator '+'

case 29: printf("+ : Operator");

state=0;

i--;

break;

 

 

//State for operator '-'

case 30: printf("+ : Operator");

state=0;

i--;

break;

 

 

//Error State

case 99: break;

}

i++;

}

printf("End of program");

getch();

}

Output of the program should be like this:

Correct input

-------------
*** Program on Lexical Analysis *** 

Enter the string: for(x1=0; x1<=10; x1++);


Analysis:
 

for     : Keyword

(       : Special character

x1      : Identifier

=       : Assignment operator

0       : Constant

;       : Special character

x1      : Identifier

<=      : Relational operator

10      : Constant

;       : Special character

x1      : Identifier

+       : Operator

+       : Operator

)       : Special character

;       : Special character

End of program

Wrong input

-----------

*** Program on Lexical Analysis ***

Enter the string: for(x1=0; x1<=19x; x++);

Analysis:

for     : Keyword

(       : Special character

x1      : Identifier

=       : Assignment operator

0       : Constant

;       : Special character

x1      : Identifier

<=      : Relational operator

Token cannot be generated