/in/foo.c: In function 'FindMaxNeg':
/in/foo.c:6:15: warning: statement with no effect [-Wunused-value]
  for(i=1;i++;i<n)
              ~^~
/in/foo.c:5:19: warning: unused variable 'j' [-Wunused-variable]
  int max=a[0],i,k,j;
                   ^
/in/foo.c:5:17: warning: unused variable 'k' [-Wunused-variable]
  int max=a[0],i,k,j;
                 ^
/in/foo.c: At top level:
/in/foo.c:13:6: warning: return type of 'main' is not 'int' [-Wmain]
 void main()
      ^~~~
/in/foo.c: In function 'main':
/in/foo.c:17:15: warning: statement with no effect [-Wunused-value]
  for(i=0;i++;i<n1)
              ~^~~
/in/foo.c:21:16: warning: statement with no effect [-Wunused-value]
   for(i=0;i++;i<n2)
               ~^~~
/in/foo.c: In function 'FindMaxNeg':
/in/foo.c:6:11: warning: iteration 2147483646 invokes undefined behavior [-Waggressive-loop-optimizations]
  for(i=1;i++;i<n)
          ~^~
/in/foo.c:6:2: note: within this loop
  for(i=1;i++;i<n)
  ^~~