Different results in Linux than in Windows C++ - c++

Question

I've created my code in Microsoft Visual Studio Express 2013 and it compiles and runs fine. I've moved this over to Linux and it gives me a different result for the GPA output. The GPA's are coming as 0 and 6.95281e-310 instead of the 3.9 and 3.5.
Also wondering if there is a difference between the strcmp and strncpy in Linux since I had to add #include <cstring> in my student.h?
Is there something else I should be using instead of strncpy in Linux?
student.h
#ifndef STUDENT_H
#define STUDENT_H
#include <iostream>
#include <cstring>
using namespace std;
class Student
{
public:
Student(const char initId[], double gpa);
bool isLessThanByID(const Student& aStudent) const;
bool isLessThanByGpa(const Student& aStudent) const;
void print()const;
private:
const static int MAX_CHAR = 100;
char id[MAX_CHAR];
double gpa;
};
#endif
student.cpp
#include "student.h"
//implement the required 3 functions here
Student::Student(const char initId[], double gpa) : gpa(gpa)
{
// initialize a newly created student object with the passed in value
strncpy(id, initId, Student::MAX_CHAR - 1);
if (Student::MAX_CHAR > 0)
{
id[Student::MAX_CHAR - 1] = '\0';
}
}
bool Student::isLessThanByID(const Student& aStudent) const
{
// compare the current student object with the passed in one by id.
if (strcmp(id, aStudent.id) > 0)
{
return true;
}
else
{
return false;
}
}
bool Student::isLessThanByGpa(const Student& aStudent) const
{
// compare the current student object with the passed in one by gpa
if (gpa < aStudent.gpa)
{
return true;
}
else
{
return false;
}
}
void Student::print() const
{
cout << id << '\t' << gpa << endl;
}
app.cpp
#include "student.h"
int main()
{
Student s1("G10", 3.9);
Student s2("G20", 3.5);
s1.print();
s2.print();
if(s1.isLessThanByID(s2))
{
cout << "about right!" << endl;
}
else
{
cout << "uhmm ..." << endl;
}
if(!s1.isLessThanByGpa(s2))
{
cout << "about right!" << endl;
}
else
{
cout << "uhmm ..." << endl;
}
//system("pause");
return 0;
}

Answer 1

strcmp compares strings http://www.cplusplus.com/reference/cstring/strcmp/
strncpy copies them http://www.cplusplus.com/reference/cstring/strncpy/
There IS a great diff really between them, in Linux and other systems as well.