/in/foo.cc: In function 'void func(int)':
/in/foo.cc:20:13: error: 'sum' was not declared in this scope
             sum++
             ^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:26:6: warning: unused variable 'sum' [-Wunused-variable]
  int sum=0;
      ^~~