Language: C

j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      | ^
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['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |     ^~~~~
main.c:1:3: error: type defaults to 'int' in declaration of 'a' [-Wimplicit-int]
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |   ^
main.c:1:12: error: type defaults to 'int' in declaration of 's' [-Wimplicit-int]
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |            ^
main.c:1:14: error: type defaults to 'int' in declaration of 'z' [-Wimplicit-int]
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |              ^
main.c:1:20: error: return type defaults to 'int' [-Wimplicit-int]
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |                    ^~~~
main.c: In function 'main':
main.c:1:20: error: type of 'i' defaults to 'int' [-Wimplicit-int]
main.c:1:63: error: lvalue required as left operand of assignment
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |                                                               ^
main.c:1:90: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |                                                                                          ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
main.c:1:90: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |                                                                                          ^~~~~
main.c:1:90: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:1:97: error: assignment to 'int' from 'char *' makes integer from pointer without a cast [-Wint-conversion]
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |                                                                                                 ^
main.c:1:97: error: passing argument 1 of 'scanf' makes pointer from integer without a cast [-Wint-conversion]
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |                                                                                                ~^~~~~~~
      |                                                                                                 |
      |                                                                                                 int
main.c:1:97: note: expected 'const char *' but argument is of type 'int'
main.c:1:110: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |                                                                                                              ^~~~~~
main.c:1:110: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:1:110: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:1:110: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:1:117: error: passing argument 1 of 'printf' makes pointer from integer without a cast [-Wint-conversion]
    1 | j,a['   '],s,z=1e6;main(i){for(;++i<998;)for(j=i*i;!a[i]&&a[j]=j<z;j+=i);for(i=1;++i<z||~scanf(s="%d\n",&j)&&printf(s,a[j]);a[i]=s+=!a[i]);}
      |                                                                                                                     ^
      |                                                                                                                     |
      |                                                                                                                     int
main.c:1:117: note: expected 'const char *' but argument is of type 'int'