Lex Program to check whether a number is Prime or Not

Problem: Write a Lex Program to check whether a number is Prime or Not.

Explanation:
Lex is a computer program that generates lexical analyzers and was written by Mike Lesk and Eric Schmidt. Lex reads an input stream specifying the lexical analyzer and outputs source code implementing the lexer in the C programming language.

Definition: A prime number is a whole number greater than 1 whose only factors are 1 and itself. A factor is a whole numbers that can be divided evenly into another number. The first few prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23 and 29.



Examples:

Input: 2 
Output: Prime number

Input: 6
Output: Not a Prime number 

Implementation:

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/* Lex Program to check whether a number is Prime or Not */
  
%{
   /* Definition section */
   #include<stdio.h>
   #include<stdlib.h>
   int flag,c,j;
%}
  
/* Rule Section */
%%
[0-9]+ {c=atoi(yytext);
         if(c==2)
         {
           printf("\n Prime number");
         }
         else if(c==0 || c==1)
         {
           printf("\n Not a Prime number");
         }
         else
         {
           for(j=2;j<c;j++)
         {  
         if(c%j==0)
           flag=1;
         }
         if(flag==1)
           printf("\n Not a prime number");
         else if(flag==0)
           printf("\n Prime number");
         }
       }
%%
  
// driver code
int main()
 {
  yylex();
  return 0;
 }

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