I'm getting an error saying, NEGATIVE RANGE IN CHARACTER CLASS in lines 15,17 and 19 - lex

Question

Please find the error in lines 15,17 and 19:
%{
#include<stdio.h>
int c=0;
FILE *fp;
%}
operator [+-*/]
identifier [a-zA-Z][a-zA-Z0-9]*
number [0-9]+
expression ({identifier}|{number}){operator}({identifier}|{number})
%%
\n { c++; }
^"#".+ ;
^("int "|"float "|"char ").+ ;
"void main()" ;
{identifier}"="({expression}+";") {printf("Valid arithmetic expression in line %d",c+1);ECHO;printf("\n");}
{identifier}"="({number}|{identifier}";") {printf("Valid assignment statement in line %d",c+1);ECHO;printf("\n");}
({number}|([0-9]+[a-zA-Z0-9]*))"="{expression}+ {printf("Invalid: rules for naming identifier are violated in line %d",c+1);ECHO;printf("\n");}
{identifier}"=;" {printf("Invalid right side of expression missing in line %d",c+1);ECHO;printf("\n");}
{operator}{operator}+ {printf("Invalid multiple operators cannot occur consecutively in line %d",c+1);ECHO;printf("\n");}
. ;
%%
main()
{
yyin=fopen("3b.txt","r");
yylex();
fclose(yyin);
}

Answer 1

I don't think that your error "Negative Range in Character Class" is actually on lines 15, 17, or 19. I believe that it is on line 6. Your code says operator [+-*/], by which you appear to mean "the symbols +, -, *, and /".
However, the - is actually being interpreted as a "range" from + to *. Since + is character 43 and * is character 42, that range is backwards.
If you escape the - with \ before it, you should not have that error anymore.