Sandeep Hegde

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System Software Lab Programs ( Lex and Yaac Programs )2a.l

// June 9th, 2009 // Educational, Engineering, Unix and System Software Lab

Subject : System Software Laboratory

Branch : Information Science & Engineering

Semester : 6

University : VTU

………………………………………………………………………………………………………………………….
PART – A

………………………………………………………………………………………………………………………….

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

%{
#include<stdio.h>
#include<string.h>
#define max 20
int flag,i,j,k,top,b;
char stack[max],ident[max],oper[max],brac[max];
%}

%%
[a-zA-Z0-9] {j++;strcat(ident,yytext);}
[a-zA-Z0-9]+ {flag=1;}
“+” {oper[k++]=’+';}
“-” {oper[k++]=’-';}
“*” {oper[k++]=’*';}
“/” {oper[k++]=’*';}
“$” {oper[k++]=’$';}
“^” {oper[k++]=’^';}
“%” {oper[k++]=’%';}
“(” { stack[++top]=’(‘;brac[b++]=’(‘;}
“)” { if (stack[top]==’(‘ && top!=-1) top–;flag=0;brac[b++]=’)';}
%%

int  main()
{
int i=j=k=b=flag=0;
top=-1;

printf(“\nEnter the Expression : “);
yylex();
printf(“\nThe identifiers are :  “);

for(i=0;i<j;i++)
printf(“\t%c”,ident[i]);

printf(“\nNo.of identifiers are : %d”,j);
printf(“\nThe operators are :\n”);

for(i=0;i<k;i++)
printf(“\t%c”,oper[i]);

printf(“\nNo. of operators are :%d”,k);
if(flag==0 && top==-1 && j==k+1)
printf(“\nValid expression”);
else
printf(“\nInvalid expression”);

return 0;
}

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