Language: C

j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
      | ^
main.c:1:1: error: type defaults to 'int' in declaration of 'j' [-Wimplicit-int]
main.c:1:5: warning: multi-character character constant [-Wmultichar]
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
      |     ^~~~~
main.c:1:3: error: type defaults to 'int' in declaration of 'a' [-Wimplicit-int]
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
      |   ^
main.c:1:12: error: return type defaults to 'int' [-Wimplicit-int]
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
      |            ^~~~
main.c: In function 'main':
main.c:1:12: error: type of 'i' defaults to 'int' [-Wimplicit-int]
main.c:1:35: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
      |                                   ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
main.c:1:35: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
      |                                   ^~~~~
main.c:1:35: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:1:42: error: assignment to 'int' from 'char *' makes integer from pointer without a cast [-Wint-conversion]
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
      |                                          ^
main.c:1:42: error: passing argument 1 of 'scanf' makes pointer from integer without a cast [-Wint-conversion]
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
      |                                         ~^~~~~~~
      |                                          |
      |                                          int
main.c:1:42: note: expected 'const char *' but argument is of type 'int'
main.c:1:54: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
      |                                                      ^~~~~~
main.c:1:54: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:1:54: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:1:54: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:1:61: error: 's' undeclared (first use in this function)
    1 | j,a['   '];main(i){for(;++i<1e6||~scanf(j="%d\n",a)&&printf(s,a[*a]);)if(!a[i])for(a[j=i]=*a+=!a[i];j<1e6;a[j+=i]=1);}
      |                                                             ^
main.c:1:61: note: each undeclared identifier is reported only once for each function it appears in