Lexical Analysis

aruljothi · Mar 31, 2009, 11:12 AM

/* Program on lexical analysis */

#include<stdio.h>
#include<conio.h>
#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<MAX; j++)
str[j]=NULL; //Initialise NULL

printf("*** Program on Lexical Analysis ***");
printf("

Enter the string: ");
gets(str); //Accept input string
str[strlen(str)]=' ';

printf("

Analysis:
");

while(str!=NULL)
{
while(str==' ') //To eliminate spaces
i++;
switch(state)
{
case 0: if(str=='i') state=1; //if
else if(str=='w') state=3; //while
else if(str=='d') state=8; //do
else if(str=='e') state=10; //else
else if(str=='f') state=14; //for
else if(isalpha(str) || str=='_')
{
    state=17;
    startid=i;
} //identifiers

else if(str=='<') state=19;
//relational '<' or '<='

else if(str=='>') state=21;
//relational '>' or '>='

else if(str=='=') state=23;
//relational '==' or assignment '='

else if(isdigit(str))
{
    state=25; startcon=i;
}
       //constant

else if(str=='(') state=26;
//special characters '('

else if(str==')') state=27;
//special characters ')'

else if(str==';') state=28;
//special characters ';'

else if(str=='+') state=29;
//operator '+'

else if(str=='-') state=30;
//operator '-'

break;

//States for 'if'
case 1: if(str=='f') state=2;
else { state=17; startid=i-1; i--; }
break;
case 2: if(str=='(' || str==NULL)
{
printf("
if    : Keyword");
state=0;
i--;
}
else { state=17; startid=i-2; i--; }
break;

//States for 'while'
case 3: if(str=='h') state=4;
else { state=17; startid=i-1; i--; }
break;
case 4: if(str=='i') state=5;
else { state=17; startid=i-2; i--; }
break;
case 5: if(str=='l') state=6;
else { state=17; startid=i-3; i--; }
break;
case 6: if(str=='e') state=7;
else { state=17; startid=i-4; i--; }
break;
case 7: if(str=='(' || str==NULL)
{
printf("
while    : Keyword");
state=0;
i--;
}
else { state=17; startid=i-5; i--; }
break;

//States for 'do'
case 8: if(str=='o') state=9;
else { state=17; startid=i-1; i--; }
break;
case 9: if(str=='{' || str==' ' || str==NULL || str=='(')
{
printf("
do    : Keyword");
state=0;
i--;
}
break;

//States for 'else'
case 10: if(str=='l') state=11;
else { state=17; startid=i-1; i--; }
break;
case 11: if(str=='s') state=12;
else { state=17; startid=i-2; i--; }
break;
case 12: if(str=='e') state=13;
else { state=17; startid=i-3; i--; }
break;
case 13: if(str=='{' || str==NULL)
{
printf("
else    : Keyword");
state=0;
i--;
}
else { state=17; startid=i-4; i--; }
break;

//States for 'for'
case 14: if(str=='o') state=15;
else { state=17; startid=i-1; i--; }
break;
case 15: if(str=='r') state=16;
else { state=17; startid=i-2; i--; }
break;
    case 16: if(str=='(' || str==NULL)
{
printf("
for    : Keyword");
state=0;
i--;
}
else { state=17; startid=i-3; i--; }
break;

//States for identifiers
case 17:

if(isalnum(str) || str=='_')
{
    state=18; i++;
}
else if(str==NULL||str=='<'||str=='>'||str=='('||str==')'||str==';'||str=='='||str=='+'||str=='-') state=18;
i--;
break;

case 18:

if(str==NULL || str=='<' || str=='>' || str=='(' || str==')' || str==';' || str=='=' || str=='+' ||str=='-')
{
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=='=') state=20;
else if(isalnum(str) || str=='_')
{
printf("
<    : Relational operator");
i--;
state=0;
}
break;
case 20: if(isalnum(str) || str=='_')
{
printf("
<=    : Relational operator");
i--;
state=0;
}
break;

//States for relational operator '>' & '>='
case 21: if(str=='=') state=22;
else if(isalnum(str) || str=='_')
{
printf("
>    : Relational operator");
i--;
state=0;
}
break;
case 22: if(isalnum(str) || str=='_')
{
printf("
>=    : Relational operator");
i--;
state=0;
}
break;

//States for relational operator '==' & assignment operator '='
case 23: if(str=='=') state=24;
else
{
printf("
=    : Assignment operator");
i--;
state=0;
}
break;
case 24: if(isalnum(str))
{
printf("
==    : Relational operator");
state=0;
i--;
}
break;

//States for constants
case 25: if(isalpha(str))
{
printf("

*** ERROR ***
");
puts(str);
for(j=0; j<i; j++)
printf(" ");
        printf("^");
printf("
Error at position %d
Alphabet cannot follow digit", i);
state=99;
}
else if(str=='(' || str==')' || str=='<' || str=='>' || str==NULL || str==';' || str=='=')
{
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: goto END;
}
i++;
}
printf("

End of program");
END:
getch();
}

/* Output

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
*/

algeraadrian · Dec 18, 2010, 01:24 AM

Lexical analysis is the process of converting a sequence of characters into a sequence of tokens. A program or a function that performs lexical analysis is called a parser, lexical or scanner. A parser is often a single function that is called by a parser or other function.

SLBS Student · Jul 06, 2013, 01:02 AM

Quote from: algeraadrian on Dec 18, 2010, 01:24 AM
Lexical analysis is the process of converting a sequence of characters into a sequence of tokens. A program or a function that performs lexical analysis is called a parser, lexical or scanner. A parser is often a single function that is called by a parser or other function.

Please don't put these type of complete code on website. because our college teachers just copy the code, and show us (students) that they have created the code . But the truth is They just copy the code, put in pen drive. and show in-front of us.
I am a 2008 batch, and due to these type of faculty (and this is the situation of India colleges) and our fake college placements, I and my friends are still weeping in this IT world for a career .
This is Incredible India boss. anything can be happens by these type of copy paste Indian Engineers.

so please put only logic on the web , not the code

Thanks
regards
SLBS Student
www.slbsjodhpur.com

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Lexical Analysis

aruljothi

algeraadrian

SLBS Student