C++ Code crashing when I reference a file - c++

Question

You can see by the "In what file is the data for the graph contained?" prompt, that I have to input a file to get the code to function properly. The program gets up to "In what file is the data for the graph contained?", then I input a file name, it freezes then crashes. My whole computer freezes and other applications begin to crash. I even ran the code by removing my own code, and the same problem occurs. What is causing this? And how can I fix this?
#include <fstream>
#include <iostream>
using namespace std;
struct edge {
struct vertex* Vertex;
int weight;
edge* nextedge;
edge(edge* e = 0, struct vertex* v = 0, int w = 0)
{
Vertex = v;
weight = w;
nextedge = e;
}
};
struct vertex {
char name;
vertex* nextvertex;
edge* edgelist;
int index;
bool final;
vertex* pre;
vertex(char n = '\0', vertex* v = 0)
{
name = n;
nextvertex = v;
edgelist = 0;
index = -1;
final = false;
pre = 0;
}
};
int main()
{
char input_file[128];
cout << "In what file is the data for the graph contained?\n> ";
cin.getline(input_file, 128);
ifstream infile(input_file);
vertex* graph = 0;
vertex *startptr = 0, *finishptr = 0;
vertex *vertexsearch = 0, *vptr = 0;
vertex* last;
vertex* w;
edge* edgeptr = 0;
int weight;
char start, finish, comma;
bool startnotfound = true, finishnotfound = true;
infile >> start >> comma >> finish >> comma >> weight;
while (!infile.eof()) {
/* build the edge list */
startptr = new vertex(sizeof(struct vertex));
finishptr = new vertex(sizeof(struct vertex));
finishptr->name = finish;
startptr->name = start;
startptr->nextvertex = finishptr;
edgeptr = new edge();
edgeptr->Vertex = startptr;
edgeptr->weight = weight;
edgeptr->nextedge = NULL;
graph = new vertex(sizeof(struct vertex));
graph->name = finish;
graph->edgelist = edgeptr;
}
// Output the graph
vptr = graph;
while (vptr) {
cout << vptr->name << '\n';
edgeptr = vptr->edgelist;
while (edgeptr) {
cout << " Edge to " << edgeptr->Vertex->name
<< " with weight " << edgeptr->weight << '\n';
edgeptr = edgeptr->nextedge;
}
vptr = vptr->nextvertex;
}
// From where to where
cout << "From where: ";
cin >> start;
cout << "to where: ";
cin >> finish;
vertex* s = graph;
startptr = finishptr = 0;
while (s) {
if (s->name == start) {
startptr = s;
}
if (s->name == finish) {
finishptr = s;
}
s = s->nextvertex;
}
if (!startptr) {
cout << "Start point given is not a valid vertex.\n";
return 1;
}
last = startptr;
last->index = 0;
last->final = true;
while (!(finishptr->final)) {
/* Search for shortest path */
}
vptr = finishptr;
if (vptr->pre)
while (vptr) {
cout << vptr->name << '\n';
vptr = vptr->pre;
}
else
cout << "No such path.\n";
return 0;
}