/in/foo.c: In function 'main':
/in/foo.c:6:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%d%d%d",&x,&y,&z);
  ^~~~~
/in/foo.c:6:2: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:6:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:7:12: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if(x%4==0 && x%100!=0 || x%400==0)
     ~~~~~~~^~~~~~~~~~~
/in/foo.c:8:3: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   printf("%d",fr(x,y,z));
   ^~~~~~
/in/foo.c:8:3: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:8:3: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:10:3: warning: incompatible implicit declaration of built-in function 'printf'
   printf("%d",f(x,y,z));
   ^~~~~~
/in/foo.c:10:3: note: include '<stdio.h>' or provide a declaration of 'printf'