C++ Program to read numbers from a File and Find the Sum

#include <iostream>
#include <fstream>
#include <cstdlib>

int main()
{
    const int SIZE = 100;  
    int a[SIZE]; 
    std::ifstream dfile("num.dat"); 
    int i;                      

    if (dfile.bad()) {
        std::cerr << "Error: Could not open numbers.dat\n";
        exit (8);
    }

    for (i = 0; i < SIZE; ++i) {
        assert(i >= 0);
        assert(i < sizeof(a)/sizeof(a[0]));

        dfile >> a[i];
    }

    int sum;  

    sum = 0;
    for (i = 0; i < SIZE; ++i) {
        assert(i >= 0);
        assert(i < sizeof(a)/sizeof(a[0]));

        sum += a[i];
    }

    std::cout << "sum of all the numbers is " << sum << '\n';
    return (0);
}