Weird vector<long> addition with '0' as '-1' - c++

Question

I'm writing a basic chess program to calculate how many sets you can make with the given chess figures. The data file:
4
22 3 5 6 2 0
1 1 1 1 1 1
8 4 4 4 1 2
5 3 3 3 0 2
The code:
#include <iostream>
#include <fstream>
#include <vector>
int main
(int argc, char *argv[])
{
std::fstream data_file;
size_t i, k;
std::vector<long> chess;
long t, n;
data_file.open("U1.txt", std::ios::in);
data_file >> n;
for (i = 0; i < n; i++)
chess.push_back(0);
for (i = 0; i < n; i++) {
for (k = 0; k < 6; k++) {
data_file >> t;
std::cout << t << " ";
chess[k] += t;
}
std::cout << std::endl;
}
data_file.close();
for (int i = 0; i < 6; i++)
std::cout << chess[i] << " ";
std::cout << std::endl;
data_file.open("U1rez.txt", std::ios::out);
data_file << n;
std::cout << n << std::endl;
data_file.close();
return EXIT_SUCCESS;
}
The output:
22 3 5 6 2 0
1 1 1 1 1 1
8 4 4 4 1 2
5 3 3 3 0 2
36 11 13 14 3 4
4
Why am I getting 3 and 4 at the end result just after 36, 11, 13 and 14 at line 5? When I print the test values I seem to get the right numbers but something goes terribly wrong in the addition of them in the vector container.

Answer 1

for (i = 0; i < n; i++)
chess.push_back(0);
.
.
.
for (i = 0; i < n; i++) {
for (k = 0; k < 6; k++) {
data_file >> t;
std::cout << t << " ";
chess[k] += t;
}
std::cout << std::endl;
}
here, you initialized n(=4) places in the vector, but here you are accessing the index 4 and 5 of the vector chess which is causing the addition problem.

Answer 2

On an unrelated note, you will have a much easier time with C++ if you let go of some of the rules imposed by C.
The C++ API uses scope-bounded resource management; i.e. there's no need to explicitly close the file handle here, since the class does this for you when its destructor is called at the end of the declared scope.
Prefer std::cout << "\n" to std::cout << std::endl, unless you actually intend to insert a newline and flush the buffer. Many C++ programmers still use printf, and I personally think that it's a lot more elegant than C++'s ugly standard solution to IO -- feel free to use printf.
Do you find your code easier to manage and read when you declare your variable where they are used (e.g. for (size_type i = 0; ... ; ...)), rather than at the beginning of your method? This also allows the compiler to potentially make better choices about register usage, since it has more information about the scopes of your temporary variables.
Here are a few features of C++11 that can also save you some time:
Automatic type inference: when the compiler can infer the type of a variable, it's not necessary for you to explicitly specify it; you can use auto instead (e.g. auto x = parse_data();).
Range-for: if you are operating on a container that provides global definitions begin() and end() (such as any standard container), then instead of this:
typedef typename container_type::const_iterator iter;
for (iter i = begin(container), iter l = end(container); i != l; ++i) { ... }
You can do this:
for (const auto& x : container) { ... }
I just wanted to give you a few quick pointers that can save you some time.