foo.cc: In function ‘int main()’:
foo.cc:9:12: error: ‘i’ was not declared in this scope
    9 |         s3[i]+=my;
      |            ^
foo.cc: At global scope:
foo.cc:13:5: error: ‘cout’ does not name a type
   13 |     cout<<s3;
      |     ^~~~
foo.cc:14:5: error: expected unqualified-id before ‘return’
   14 |     return 0;
      |     ^~~~~~
foo.cc:15:1: error: expected declaration before ‘}’ token
   15 | }
      | ^