/in/foo.cc: In function 'int main()':
/in/foo.cc:16:25: error: 's' was not declared in this scope
   16 |                         s+=char(a[i]+'0');
      |                         ^
/in/foo.cc:17:27: error: 's' was not declared in this scope; did you mean 's2'?
   17 |                 string s2=s;
      |                           ^
      |                           s2