/in/foo.cc: In function 'int main()':
/in/foo.cc:7:18: error: 'strlen' was not declared in this scope
  int n1=strlen(s1),n2=strlen(s2);
                  ^
/in/foo.cc:10:16: error: 'n2' was not declared in this scope
  for(int i=0,j=n2-1;i<n2;i++,j--)
                ^~
/in/foo.cc:12:9: error: 'n2' was not declared in this scope
  if(n1>=n2)
         ^~