/in/foo.c: In function 'main':
/in/foo.c:14:3: warning: 'c' may be used uninitialized in this function [-Wmaybe-uninitialized]
  c+=sqrt((a[n-1]-a[0])*(a[n-1]-a[0])+(b[n-1]-b[0])*(b[n-1]-b[0]));
   ^~