http://www.cppreference.com/wiki/c/io/scanf

The return value of scanf() is the number of variables that were successfully assigned values, or EOF if there is an error

void     Readinp()
{
         int x,y;
         memset(a,0,sizeof(a));
         memset(b,0,sizeof(b));
         while (cin >> x >>y)
               {
                    a[x][y]=1;  a[y][x]=1;
                    b[x]++;    b[y]++;
                    n=max(n,max(x,y));
               }
}