Untitled

%{
#include <stdio.h>
int total = 0;
%}

%%
[0-9]+    { total += atoi(yytext); }
[-+*/\n] { /* Do nothing */ }
.        { printf("Invalid input\n"); }
%%

int main()
{
    yylex();
    printf("Result: %d\n", total);
    return 0;
}