Language: C

a[],i;
c(int*a){a=*1[&a]-*a;}
main(){~scanf("%d",a+(i++))&&main(qsort(a,10,4,c))||exit(!printf("%d\n%d\n%d\n",*a,a[1],a[2]));}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | a[],i;
      | ^
main.c:1:1: error: type defaults to 'int' in declaration of 'a' [-Wimplicit-int]
main.c:1:5: error: type defaults to 'int' in declaration of 'i' [-Wimplicit-int]
    1 | a[],i;
      |     ^
main.c:2:1: error: return type defaults to 'int' [-Wimplicit-int]
    2 | c(int*a){a=*1[&a]-*a;}
      | ^
main.c: In function 'c':
main.c:2:11: error: assignment to 'int *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
    2 | c(int*a){a=*1[&a]-*a;}
      |           ^
main.c: At top level:
main.c:3:1: error: return type defaults to 'int' [-Wimplicit-int]
    3 | main(){~scanf("%d",a+(i++))&&main(qsort(a,10,4,c))||exit(!printf("%d\n%d\n%d\n",*a,a[1],a[2]));}
      | ^~~~
main.c: In function 'main':
main.c:3:9: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    3 | main(){~scanf("%d",a+(i++))&&main(qsort(a,10,4,c))||exit(!printf("%d\n%d\n%d\n",*a,a[1],a[2]));}
      |         ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | a[],i;
main.c:3:9: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    3 | main(){~scanf("%d",a+(i++))&&main(qsort(a,10,4,c))||exit(!printf("%d\n%d\n%d\n",*a,a[1],a[2]));}
      |         ^~~~~
main.c:3:9: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:3:35: error: implicit declaration of function 'qsort' [-Wimplicit-function-declaration]
    3 | main(){~scanf("%d",a+(i++))&&main(qsort(a,10,4,c))||exit(!printf("%d\n%d\n%d\n",*a,a[1],a[2]));}
      |                                   ^~~~~
main.c:3:53: error: implicit declaration of function 'exit' [-Wimplicit-function-declaration]
    3 | main(){~scanf("%d",a+(i++))&&main(qsort(a,10,4,c))||exit(!printf("%d\n%d\n%d\n",*a,a[1],a[2]));}
      |                                                     ^~~~
main.c:1:1: note: include '<stdlib.h>' or provide a declaration of 'exit'
  +++ |+#include <stdlib.h>
    1 | a[],i;
main.c:3:53: warning: incompatible implicit declaration of built-in function 'exit' [-Wbuiltin-declaration-mismatch]
    3 | main(){~scanf("%d",a+(i++))&&main(qsort(a,10,4,c))||exit(!printf("%d\n%d\n%d\n",*a,a[1],a[2]));}
      |                                                     ^~~~
main.c:3:53: note: include '<stdlib.h>' or provide a declaration of 'exit'
main.c:3:59: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    3 | main(){~scanf("%d",a+(i++))&&main(qsort(a,10,4,c))||exit(!printf("%d\n%d\n%d\n",*a,a[1],a[2]));}
      |                                                           ^~~~~~
main.c:3:59: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:3:59: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:3:59: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:3:53: error: void value not ignored as it ought to be
    3 | main(){~scanf("%d",a+(i++))&&main(qsort(a,10,4,c))||exit(!printf("%d\n%d\n%d\n",*a,a[1],a[2]));}
      |                                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.c: At top level:
main.c:1:1: warning: array 'a' assumed to have one element
    1 | a[],i;
      | ^