/in/foo.c: In function 'main':
/in/foo.c:6:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%d%d%d%d",&b1,&a1,&b2,&a2);
  ^~~~~
/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:21:2: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
  printf("%d %d",b,a);
  ^~~~~~
/in/foo.c:21:2: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:21:2: note: include '<stdio.h>' or provide a declaration of 'printf'