/in/foo.c: In function 'main':
/in/foo.c:8:17: error: 'j' undeclared (first use in this function)
    8 |                 j=1;
      |                 ^
/in/foo.c:8:17: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:16:17: error: 'i' undeclared (first use in this function)
   16 |                 i=b*10+a;
      |                 ^
/in/foo.c:34:17: error: 'd' undeclared (first use in this function)
   34 |                 d=((n%1000)%100)%10;
      |                 ^
/in/foo.c:36:51: error: 'J' undeclared (first use in this function)
   36 |                 printf("%d\n,%d ,%d ,%d ,%d\n,%d",J,a,b,c,d,i);
      |                                                   ^
/in/foo.c:4:23: warning: unused variable 'f' [-Wunused-variable]
    4 |         int n,a,b,c,e,f;
      |                       ^