foo.cc: In function 'int f(int, int)':
foo.cc:23:14: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
       while(t=a%b)
             ~^~~~
foo.cc: In function 'int main()':
foo.cc:5:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
      int x;scanf("%d",&x);
            ~~~~~^~~~~~~~~

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