Day of the Programmer- HackerRank problem

Lex is a computer program that generates lexical analyzers. Lex reads an input stream specifying the lexical analyzer and outputs source code implementing the lexer in the C programming language.

Code:

 % {

  int op = 0,i;

  float a, b;

% }

  

dig [0-9]+|([0-9]*)"."([0-9]+)

add "+"

sub "-"

mul "*"

div "/"

pow "^"

ln \n

%%

  

/* digi() is a user defined function */

{dig} {digi();} 

{add} {op=1;}

{sub} {op=2;}

{mul} {op=3;}

{div} {op=4;}

{ln} {printf("\n The Answer :%f\n\n",a);}

  

%%

digi()

{

 if(op==0)

  

/* atof() is used to convert 

      - the ASCII input to float */

 a=atof(yytext); 

  

 else

 {

 b=atof(yytext);

  

 switch(op)

 {

   case 1:a=a+b;

    break;

  

   case 2:a=a-b;

   break;

   

   case 3:a=a*b;

   break;

   

   case 4:a=a/b;

   break;

  }

 op=0;

 }

}

  

main(int argv,char *argc[])

{

 yylex();

}

  

yywrap()

 {

  return 1;

 }