Lex Programs 2

1. Program to recognize whether a given sentence is simpler or compound.

Sim.l

%{

#include<stdio.h>

int is_simple=1;

%}

%%

[a-zA-Z0-9]+[ \t\n]+[aA][nN][dD][ \t\n]+[a-zA-Z0-9]+ {is_simple=0;}

[a-zA-Z0-9]+[ \t\n]+[oO][rR][ \t\n]+[a-zA-Z0-9]+ {is_simple=0;}

[a-zA-Z0-9]+[ \t\n]+[bB][uU][tT][ \t\n]+[a-zA-Z0-9]+ {is_simple=0;}

. {;}

%%

main()

{

printf("Enter the sentence\n");

yylex();

if(is_simple==1)

{

printf("\nThe given sentence is simple\n");

}

else

{

printf("\nThe given sentence is compound\n");

}

}

 

2.  Program to recognize and count the number of identifiers in a given input file.

Ide.l

%{

#include<stdio.h>

int count=0;

%}

var ([a-z]|[0-9]|"_")+

id "_"*{var}

%x chk c2 c3

%%

^("int"|"float"|"char"|"double") BEGIN(chk);

<chk>" "+ BEGIN(c2);

<c2>[,] BEGIN(c3);

<c2>[ ]

<c2>{id} {count++;}

<c3>{id} {count++;}

<c3>","

<c3>[;] {BEGIN(INITIAL);}

.|\n

%%

main()

{

 yyin=fopen("in.c","r");

 yylex();

 printf("No. of identifier are:%d\n",count);

}

In.c

#include<stdio.h>

void main()

{

int d,e;

float   as ,   asd ;

printf("printf("b");");

d=e;

scanf("enter %d",&d);

}

3.Program to recognize a valid arithmetic expression and identify the identifiers and operators present. Print them separately

%{

#include<stdio.h>

int flag=1;

int op=0,dig=0,top=-1;

char st[10];

%}

digit [0-9]+

oper [+*/-]

%%

['('] {st[++top]='(';}

[')'] {flag=1;

            if((st[top]!='(') && (top!=-1))

            {

                        printf("\n Invalid Expression\n");

                        exit(0);

            }

            top--;

}

{digit} {dig++;}

{oper}/{digit} {op++;}

{oper}/['('] {op++;}

. {printf("\nInvalid Expression"); exit(0);}

%%

main()

{

 printf("\nEnter arithmetic expression\n");

 yylex();

 if(((op+1==dig) || (op==dig)) && (top==-1))

 {

  printf("\nValid Expression\n");

  printf("\nNo. of operators=%d\nno. of operands=%d\n",op,dig);

 }

 else

   printf("\nInvalid expression");

}

 

 Thank You For Reading.

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