How to establish all the possible tracks

Question

In the given file named "data.in" are written the number of cities N, two cities A and B and the existing roads between them.Ex, the set "2 6" says that between city 2 and city 6 there exist a road.I have to show in a file named"data.out" all the possibilities to reach city B from city A without going more than once through a city. I have written the following code ,but it doesnt print anything.

#include <stdio.h>
#include <stdlib.h>

FILE*in;
FILE*out;
int a[101][101],s[100];
int N,A,B;

void read(int *N,int *A,int *B)
{
    int x,y;
    fscanf(in,"%d%d%d",N,A,B);

    do
    {
        fscanf(in,"%d%d",&x,&y);
        if(!feof(in))
            a[x][y]=a[y][x]=1;
    }
    while(!feof(in));
}
void print(int k)
{
    int i;
    for(i=0; i<=k; i++)
        fprintf(out,"%d ",s[i]);
    fprintf(out,"\n");
}

void BKT(int k)
{
    int i;
    for(i=1; i<=N; i++)
    {
        s[k]=i;
        if (pass(k))
            if(s[k]==B) print(k);
            else BKT(k+1);
    }
}

int pass(int k)
{
    int i;
    for(i=0; i<k; i++)
        if(s[k]==s[i]) return 0;

    if(!a[s[k]][s[k-1]]) return 0;
    return 1;
}

int main()
{
    int N,A,B;
    in=fopen("data.in","r");
    out=fopen("data.out","w");
    read(&N,&A,&B);
    s[0]=A;
    BKT(1);

    return 0;
}