Simple Number Scanner

void number (TOKEN tok)
  { long num;
    int  c, charval;
    num = 0;
    while ( (c = peekchar()) != EOF
            && CHARCLASS[c] == NUMERIC)
      {   c = getchar();
          charval = (c - '0');
          num = num * 10 + charval;
        }
    tok->tokentype = NUMBERTOK;
    tok->basicdt = INTEGER;
    tok->intval = num;
  }