ERROR:
voter.cpp: In member function 'bool VoterProgram::Voter::operator<(const VoterProgram::Voter&) const':
voter.cpp:54: error: passing 'const VoterProgram::Voter' as 'this' argument of 'int VoterProgram::Voter::get_voter_number_int()' discards qualifiers

CODE:
int VoterProgram::Voter::get_voter_number_int()
{
	return voter_number;
}

bool VoterProgram::Voter::operator< (const VoterProgram::Voter& v)
const {
	if(voter_number<v.get_voter_number_int()) return true;
	else return false;
}