/in/foo.c: In function 'main':
/in/foo.c:4:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%d%d",&x,&y);
  ^~~~~
/in/foo.c:4:2: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:4:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:7:10: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   case 1:printf("31");break;
          ^~~~~~
/in/foo.c:7:10: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:7:10: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:8:20: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   case 2:if(x%4==0 && x%100!=0 || x%400==0)
             ~~~~~~~^~~~~~~~~~~