Language: C

a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
      | ^
main.c:1:1: error: type defaults to 'int' in declaration of 'a' [-Wimplicit-int]
main.c:1:7: error: type defaults to 'int' in declaration of 'i' [-Wimplicit-int]
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
      |       ^
main.c:1:9: error: return type defaults to 'int' [-Wimplicit-int]
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
      |         ^~~~
main.c: In function 'main':
main.c:1:9: error: type of 'j' defaults to 'int' [-Wimplicit-int]
main.c:1:45: error: implicit declaration of function 'getchar' [-Wimplicit-function-declaration]
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
      |                                             ^~~~~~~
main.c:1:1: note: 'getchar' is defined in header '<stdio.h>'; this is probably fixable by adding '#include <stdio.h>'
  +++ |+#include <stdio.h>
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
main.c:1:59: error: implicit declaration of function 'exit' [-Wimplicit-function-declaration]
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
      |                                                           ^~~~
main.c:1:1: note: include '<stdlib.h>' or provide a declaration of 'exit'
  +++ |+#include <stdlib.h>
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
main.c:1:59: warning: incompatible implicit declaration of built-in function 'exit' [-Wbuiltin-declaration-mismatch]
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
      |                                                           ^~~~
main.c:1:59: note: include '<stdlib.h>' or provide a declaration of 'exit'
main.c:1:59: error: void value not ignored as it ought to be
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
      |                                                           ^~~~~~~
main.c:1:126: error: implicit declaration of function 'puts' [-Wimplicit-function-declaration]
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
      |                                                                                                                              ^~~~
main.c:1:126: note: include '<stdio.h>' or provide a declaration of 'puts'
main.c:1:131: error: passing argument 1 of 'puts' from incompatible pointer type [-Wincompatible-pointer-types]
    1 | a[11],i;main(j){for(;;){for(i=11;i--;)(a[i]=getchar())+1||exit(0);for(i=10;--i;)for(j=0;j++<i;)a[j]+=a[j+1];i=(a[1]-6)%10+48;puts(&i);}}
      |                                                                                                                                   ^~
      |                                                                                                                                   |
      |                                                                                                                                   int *
main.c:1:131: note: expected 'const char *' but argument is of type 'int *'