/in/foo.c: In function 'main':
/in/foo.c:29:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%s",&arr);
  ^~~~~
/in/foo.c:29:2: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:29:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:29:10: warning: format '%s' expects argument of type 'char *', but argument 2 has type 'char (*)[100]' [-Wformat=]
  scanf("%s",&arr);
          ^
/in/foo.c:32:2: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
  printf("%d",num);
  ^~~~~~
/in/foo.c:32:2: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:32:2: note: include '<stdio.h>' or provide a declaration of 'printf'