C++-程序结束时出现分段错误

所以我有这个程序，它运行并做它应该做的事情。但在执行结束时，它抛出了一个分段错误。我运行了调试器，它说："程序收到信号SIGSEGV，分段错误"。我一行一行地运行调试器，当一切完成时，它似乎在主函数中抛出了错误。

代码：

#include <string>
#include <iostream>
#include <fstream>
#include <sstream>
#include <cstdlib>
using namespace std;
const int MAX = 100;
int firstDigit = 0; //vertex number
int verticesCount = 0;
int adjVerticesCount = 0;
class graph
{
    private:
        int n;
        int data[MAX];
        int gptr[MAX][MAX];
    public:
        void create();
        void cleanupMatrix();
        void topological();
};
void graph::create()
{
    cleanupMatrix(); // initialize the adj matrix with zeros
    ifstream infile ("input.txt");
    string line, line_separated;

    if (infile.is_open())
    {
        while (infile.good())
        {
            while(getline(infile,line)) //reads a line
            {
                if(line.length() == 0)
                {
                    n = verticesCount;
                    topological();
                    verticesCount = 0;
                    continue;
                }
                istringstream iss(line);
                while(getline(iss, line_separated, ' '))    //separate numbers in each line read
                {
                    //convert string digit to int digit
                    int temp; 
                    temp = atoi(line_separated.c_str());
                    if(firstDigit == 0) //On each line the first digit is the vertex. The rest is the adjacency vertices
                    {
                        firstDigit = temp;
                        verticesCount++;
                        data[firstDigit] = firstDigit;
                    }
                    else
                    { //pointing the g array to linked list containing adjacency vertices   
                        adjVerticesCount++;
                        gptr[firstDigit][temp] = 1;
                    }
                }
                adjVerticesCount = 0;
                firstDigit = 0;
            }
                n = verticesCount;
                topological();
                verticesCount = 0;
        }
        infile.close();
    }
    else
    {
        cout << "Error: Could not open file 'input.txt'" << endl; //oopsi.. where is the file?
    }
}
void graph::cleanupMatrix()
{
    int x,y;
    for(x=1;x<=MAX;x++)
        for(y=1;y<=MAX;y++)
            gptr[x][y] = 0;
}
void graph::topological()
{
    int flag;
    int i,j;
    int poset[MAX],included[MAX];
    for(i=1;i<=n;i++)
    {
        poset[i]=0;
        included[i]=false;
    }
    int k = 1;
    flag = true;
    int zeroindegree;
    int c = 1;
    while(flag==1)
    {
        for(i=1;i<=n;i++)
        {
            if(!included[i])
            {
                zeroindegree=true;
                for(j=1;j<=n;j++)
                {
                    if(gptr[j][i]>0)
                    {
                        zeroindegree=false;
                        break;
                    }
                }
                if(zeroindegree)
                {
                    included[i]=true;
                    poset[k]=data[i];
                    k=k+1;
                    for(j=1;j<=n;j++)
                    {
                        gptr[i][j]=-1;
                        gptr[j][i]=-1;
                    }
                    break;
                }
            }
        }
        if(i==n+1)
        {
            if(zeroindegree==false)
            {
                cout<<"Graph is not acyclicn";
                return;
            }
            else
            {
                poset[k]=data[i-1];
                k=k+1;
               flag=false;
            }
        }
    }
    ofstream outFile;
    outFile.open("output.txt", ios_base::app);
    cout << "Topological sorting:n";
    outFile << "Topological sorting:n";
    for(i=1;i<=n;i++)
    {
        cout << poset[i];
        outFile << poset[i];
        if(i != n)
        {
            cout << ", ";
            outFile << ", ";
        }
    }
    cout << "n" << endl;
    outFile << "n" << endl;
    outFile.close();
    cleanupMatrix();
}
int main()
{
    //Clear the output file
    fstream file;
    file.open("output.txt", fstream::out | fstream::trunc);
    file.close();
     graph obj;
     obj.create();
}

我做错了什么？