foo.cc: In function ‘int main()’:
foo.cc:7:9: warning: this ‘for’ clause does not guard... [-Wmisleading-indentation]
    7 |         for(int i=s.size()-1;i>=0;i--);
      |         ^~~
foo.cc:8:9: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘for’
    8 |         {
      |         ^
foo.cc:9:27: error: ‘i’ was not declared in this scope
    9 |                 if('0'<=s[i]&&s[i]<='9')
      |                           ^