/in/foo.c: In function 'main':
/in/foo.c:4:3: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   printf("ckw");
   ^~~~~~
/in/foo.c:4:3: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:4:3: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:5:2: warning: incompatible implicit declaration of built-in function 'printf'
  printf("\n");
  ^~~~~~
/in/foo.c:5:2: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:8:8: error: 'i' undeclared (first use in this function)
   for( i=0;i<11;i++)
        ^
/in/foo.c:8:8: note: each undeclared identifier is reported only once for each function it appears in