/in/foo.cc: In function 'int main()':
/in/foo.cc:12:16: error: 'strlen' was not declared in this scope
  l1 = strlen(a1);
                ^
/in/foo.cc:14:23: warning: left operand of comma operator has no effect [-Wunused-value]
  for (i = 0,j=l1-1; i < l1,j>=0; i++,j--)
                     ~~^~~~
/in/foo.cc:16:23: warning: left operand of comma operator has no effect [-Wunused-value]
  for (i = 0,j=l2-1; i < l2,j>=0; i++,j--)
                     ~~^~~~