Opening 2 data files with c++

Opening 2 data files with c++

I wrote a program to create gnuplot commands according to data that was
read from an input file. I required far too many commands to do this by
hand. This worked quite nicely, but I now need to read data from two
different data files and use these to create the gnuplot commands.
Unfortunately something now seems to be going wrong with the reading of
the two files. The portion of code involved in reading from the data files
is as follows:
#include <iostream>
#include <fstream>
#include <sstream>
using namespace std;
int n_snapshots;
int main () {
std::cout << "Enter number of snapshots" << "\n";
std::cin >> n_snapshots;
int snap_cell_count[n_snapshots];
std::ifstream in_file_count("data/snapshot_data");
std::ifstream in_file_fates("data/cell_fates_data_final");
for (int i=0; i<n_snapshots; i++) {
in_file_count >> snap_cell_count[i];
}
in_file_count.close();
int cell_fates[snap_cell_count[n_snapshots-1]];
for (int i=0; i<snap_cell_count[n_snapshots-1]; i++) {
in_file_fates >> cell_fates[i];
}
in_file_fates.close();
n_snapshots is simply some integer, snap_cell_count[] is an array with
"n_shapshots" elements, each of which takes a value read from the data
file "snapshot_data". cell_fates[] is an array with a number of elements
that is equal to the value of the last element in snap_cell_count[], and
again the values of its elements are read from a file, in this case
"cell_fates_data_final". The data files to be read from are stored in a
folder called "data".
Unfortunately, the compiler returns the following errors.
Undefined symbols for architecture x86_64:
"std::basic_string<char, std::char_traits<char>, std::allocator<char>
>::c_str() const", referenced from:
_main in ccrpSAv5.o
"std::basic_stringstream<char, std::char_traits<char>,
std::allocator<char> >::str() const", referenced from:
_main in ccrpSAv5.o
"std::basic_istream<char, std::char_traits<char> >::operator>>(int&)",
referenced from:
_main in ccrpSAv5.o
"std::basic_ostream<char, std::char_traits<char> >::operator<<(int)",
referenced from:
_main in ccrpSAv5.o
"std::basic_string<char, std::char_traits<char>, std::allocator<char>
>::~basic_string()", referenced from:
_main in ccrpSAv5.o
"std::basic_ifstream<char, std::char_traits<char> >::close()",
referenced from:
_main in ccrpSAv5.o
"std::basic_ifstream<char, std::char_traits<char> >::basic_ifstream(char
const*, std::_Ios_Openmode)", referenced from:
_main in ccrpSAv5.o
"std::basic_ifstream<char, std::char_traits<char> >::~basic_ifstream()",
referenced from:
_main in ccrpSAv5.o
"std::basic_ofstream<char, std::char_traits<char> >::open(char const*,
std::_Ios_Openmode)", referenced from:
_main in ccrpSAv5.o
"std::basic_ofstream<char, std::char_traits<char> >::close()",
referenced from:
_main in ccrpSAv5.o
"std::basic_ofstream<char, std::char_traits<char> >::basic_ofstream()",
referenced from:
_main in ccrpSAv5.o
"std::basic_ofstream<char, std::char_traits<char> >::~basic_ofstream()",
referenced from:
_main in ccrpSAv5.o
"std::basic_stringstream<char, std::char_traits<char>,
std::allocator<char> >::basic_stringstream(std::_Ios_Openmode)",
referenced from:
_main in ccrpSAv5.o
"std::basic_stringstream<char, std::char_traits<char>,
std::allocator<char> >::~basic_stringstream()", referenced from:
_main in ccrpSAv5.o
"std::ios_base::Init::Init()", referenced from:
__static_initialization_and_destruction_0(int, int) in ccrpSAv5.o
"std::ios_base::Init::~Init()", referenced from:
__static_initialization_and_destruction_0(int, int) in ccrpSAv5.o
"std::cin", referenced from:
_main in ccrpSAv5.o
"std::cout", referenced from:
_main in ccrpSAv5.o
"std::basic_ostream<char, std::char_traits<char> >& std::operator<<
<std::char_traits<char> >(std::basic_ostream<char,
std::char_traits<char> >&, char const*)", referenced from:
_main in ccrpSAv5.o
"___gxx_personality_v0", referenced from:
Dwarf Exception Unwind Info (__eh_frame) in ccrpSAv5.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
This is being compiled with the gcc compiler on Mac OSX Mountain Lion.
Does anyone have any idea what's wrong here?
Thanks very much.