Function to generate a random weighted graph freezes after a certain threshold edges

So I'm trying to generate a random graph with n nodes and n*4 edges by having the nodes 1, 2, 3, ..., n and the edges being an array of triples which stores endpoint of edge 1, endpoint of edge 2 and the weight of the edge:

struct edge{
    int endpoint1;
    int endpoint2;
    int weight;
};

This is the function to generate the array of edges (of triples):

edge* generateRandomGraph(int nrOfNodes)
{
    int adjMatrix[nrOfNodes+1][nrOfNodes+1] = {0};

    int nrOfEdges = nrOfNodes*4 ;

    edge *edges = new edge[nrOfNodes+1];
    
    int counter = 0;

    while(counter < nrOfEdges)
    {
        int a = 1 + rand() % nrOfNodes;
        int b = 1 + rand() % nrOfNodes;

        if(a != b)
        if(adjMatrix[a][b] == 0)
        {
            adjMatrix[a][b] = 1;
            adjMatrix[b][a] = 1;
            edges[counter].endpoint1 = a;
            edges[counter].endpoint2 = b;
            edges[counter].weight = rand() % 100;
            counter++;
        }
    }
                        
    return edges;
}

It functions properly until one point, at element edges[31] when it freezes. What could be the problem? Debugger does not specify any error, but when I try to print the values it breaks. Maybe some segmentation fault because the filling of the array is based on the rand()?