As it was said by others DBL_MAX
defined in header <cfloat>
in C++ or <float.h>
in C is the value of maximum representable finite floating-point (double) number
In C++ you can get the same value using class std::numeric_limits
defined in header <limits>
std::numeric_limits<double>::max()
Here is an example of using the both approaches
#include <iostream>
#include <cfloat>
#include <limits>
int main()
{
std::cout << DBL_MAX << std::endl;
std::cout << std::numeric_limits<double>::max() << std::endl;
return 0;
}
At www.ideone.com (on-line C++ compiler) the output is
1.79769e+308
1.79769e+308