Throwing and Catching exceptions with a template class - c++

Question

What I'm trying to create is a TestScore Template class that just simply calculates the average of a array. I'm trying to throw a exception when a grade is negative or bigger than 100. I have created a NegativeScore exception class and a TooLargeScore exception class,both which just return a string message. In main, i create my array and ask the user for the grades, then use the class to get the average but for some reason it doesnt find the average. It doesnt print out the average when i try to. Im thinking the problem lies with my pointers but i dont know what the exact problem is, anyone know?
#ifndef TESTSCORES_H_INCLUDED
#define TESTSCORES_H_INCLUDED
#include <iostream>
#include "NegativeScore.h"
#include "TooLargeScore.h"
#include <iomanip>
using namespace std;
template <class T>
class TestScores
{
private:
T* testscores[];
public:
TestScores(T testscores[]);
T GetAverage();
};
template <class T>
TestScores<T>::TestScores(T testscores[])
{
*(this->testscores) = testscores;
}
template <class T>
T TestScores<T>::GetAverage()
{
T average;
T sum;
T counter;
for(int i = 0; i <= 5; i++)
{
if(*testscores[i] < 0)
{
throw NegativeScore("Test Score is negative, its invalid!");
}
else if(*testscores[i] > 100)
{
throw TooLargeScore("Test score it too high, its invalid!");
}
else
{
sum = sum + *testscores[i];
}
counter++;
}
average = sum / 5;
return average;
}
MAIN
int main()
{
int MAX = 5;
double scores[MAX];
for(int i = 0; i < MAX; i++)
{
int score;
cout << "Enter the test score for test "<< (i+1) << endl;
cin >> score;
scores[i] = score;
}
try
{
TestScores<double> tests(scores);
tests.GetAverage();
cout << tests.GetAverage() << endl;
}
catch(NegativeScore ex)
{
cout << ex.getMessage() << endl;
}
catch(TooLargeScore ex2)
{
cout << ex2.getMessage() << endl;
}
return 0;
}

Answer 1

Your problem is that you class holds an array of pointer to T, but you attempt to initialize it with a array of double (i.e. array of T values).
template <class T>
class TestScores
{
private:
T* testscores[];
public:
TestScores(T testscores[]);
T GetAverage();
};
template <class T>
TestScores<T>::TestScores(T testscores[])
{
*(this->testscores) = testscores; // <--- This is not doing what you think it is.
}
I am surprised that compiled, and you should strongly consider using a better compiler that will warn you of dubious operations.
You should change the class to hold a plain pointer-to-T, i.e. a T* testscores;, or better, an std::vector<T>.
For example, I could get your code working with this change:
template <class T>
class TestScores
{
private:
T* testscores; // Note simpler pointer to first element of array of length of 5.
public:
TestScores(T testscores[]);
T GetAverage();
};
You also have an error in the limits of your for loop in GetAverage (should not include 5), and your variables in that function are uninitialized and may hold garbage values.