%{
  #include<stdio.h>
  #include<stdlib.h>
  int result=0;
  int curr=0;
  char op='+';
  void apply_operation();
%}
%option noyywrap
digit [0-9]+
space [ \t]
%%
{space};
{digit}+ {
        curr=atoi(yytext);
        apply_operation();
        }
"+" {op='+';}
"-" {op='-';}
"*" {op='*';}
"/" {op='/';}
\n {
  printf("Result:%d",result);
  result=0;
  curr=0;
  op='+';
}
. {printf("Invalid character\n");
  exit(1);
}
%%
void apply_operation(){
  switch(op){
    case '+': result+=curr;break;
    case '-': result-=curr;break;
    case '*':result*=curr;break;
    case '/':{
      if(curr==0){
        printf("Error division by 0\n");
        exit(1);
      }
      result/=curr;break;
    }
    
  }
}
int main(){
  printf("Enter expression: ");
  yylex();
  return 0;
}