Adjacency matrix building function crashes with some graphs

Question

I have this function that reads a graph from a file formatted this way: numVerticies numEdges on the first line

starting vertex ending vertex edge color for each edge one per line

so it looks like this: 5 6

1 2 C

2 3 W

and so on...

C means crimson, w means white. It works for some graphs, but for others I get a seg fault. Could you please take a look at my code and tell me what's wrong with it? Here's a graph that works fine: https://i.stack.imgur.com/mPzx7.gif

Here's a one that doesnt work: https://upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Undirected_graph.svg/462px-Undirected_graph.svg.png

My code:

//reading the graph the graph from the file and building an adj. matrix for it
    int** read_graph(ifstream &fin, int &size) {
    fin >> size;  //reading the number of verticies
    int edges;
    fin >> edges;  //num of edges
    int** graph = new int*[size]; 
    for (int i = 0; i < size; i++) {  //creating the matrix
        graph[i] = new int[size];
        for (int j = 0; j < size; j++) {
            if (i == j) graph[i][j] = 0;  //0 if row and col match
            else graph[i][j] = INT_MAX;
          }  //inf otherwise
    }
    for (int i = 0; i < edges; i++) {   //reading the edges
        int vert1, vert2;
        char edge;
        fin >> vert1 >> vert2 >> edge;
        cout<<"ALIVE "<<vert1<<vert2<<endl;
        //if Crimson - 1, else - MAX_EDGE
        graph[vert1][vert2] = graph[vert2][vert1] = edge == 'C' ? 1 : MAX_EDGE;
        cout<<"ALIVE END"<<endl;
    }
    return graph;
}

Answer 1

I found the bug. If the naming of my verticies start from 0, no crashing occurs. If they start from one, the final run of the final cycle tries to access an area thats undefined.