foo.c: In function ‘FindMiSecondMax’:
foo.c:28:22: warning: ‘index’ may be used uninitialized [-Wmaybe-uninitialized]
   28 |         if(arr[i]>arr[index]&&arr[i]!=arr[index_max])
      |                      ^
foo.c:5:23: note: ‘index’ was declared here
    5 |     int i,index_max=0,index;
      |                       ^~~~~