foo.c: In function 'main':
foo.c:6:10: warning: format '%d' expects argument of type 'int *', but argument 2 has type 'long long int *' [-Wformat=]
  scanf("%d %d",&a,&b);
         ~^     ~~
         %lld
foo.c:6:13: warning: format '%d' expects argument of type 'int *', but argument 3 has type 'long long int *' [-Wformat=]
  scanf("%d %d",&a,&b);
            ~^     ~~
            %lld
foo.c:7:11: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long long int' [-Wformat=]
  printf("%d",a+b);
          ~^  ~~~
          %lld
foo.c:6:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d",&a,&b);
  ^~~~~~~~~~~~~~~~~~~~

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