Hi, I'm experimenting with the boost lambda library, and I wrote the following code, to go through the vector of numbers and print out statements if the number is greater than 5 or less than 5 int a[]={1,2,3,4,5,6,7,8,9,10,10,9,8,4,7,6,5,4,3,3,1}; std::vector<int> v(a,a+sizeof(a)/sizeof(int)); std::for_each ( v.begin() , v.end() , (if_(_1<5)[ std::cout<<var((boost::format("%d is less than 5\n")%_1).str()) ].else_[ std::cout<<var((boost::format("%d is greater than 5\n")%_1).str()) ]) ); The boost::basic_format::operator % code gives an assertion since the object that is being passed is the placeholder object, and not the current value. Is there a correct way of doing this? Thanks, Haroon