foo.c: In function 'main':
foo.c:15:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%s",line);
  ^~~~~~~~~~~~~~~~
foo.c: In function 'cal':
foo.c:91:19: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized]
  stack_n[top_n++] = res;
  ~~~~~~~~~~~~~~~~~^~~~~
foo.c: In function 'main':
foo.c:54:19: warning: 'temp' may be used uninitialized in this function [-Wmaybe-uninitialized]
    stack_n[top_n] = temp;
    ~~~~~~~~~~~~~~~^~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。