If you are using a compiler with c++11 support in it, you can use the to_string method that chris mentioned (http://www.cplusplus.com/reference/string/to_string/?kw=to_string)
DrawScreenString(1,5, "Lives Remaining: " + std::to_string(livesRemaining), 0xF00000, NULL).
However, if your compiler doesn't have the to_string functionality, you can use a stringstream to construct (http://www.cplusplus.com/reference/sstream/stringstream/stringstream/) or sprintf into a char buffer and then constructing the string from a char buffer. I personally don't like the sprintf option because of the fixed buffer and concerns about overflow of the buffer if the input isn't checked, but it is an option.
Edit: Example with stringstream added per OP request:
#include <sstream>
...
std::stringstream ss;
int livesRemaining = 5;
ss << "Lives remaining: " << livesRemaining;
DrawScreenString(1,5, ss.str(), 0xF00000, NULL);