foo.c: In function 'main':
foo.c:50:34: error: 'k' undeclared (first use in this function)
   if(num[i]==max)printf("%s\n",n[k].max);
                                  ^
foo.c:50:34: note: each undeclared identifier is reported only once for each function it appears in
foo.c:52:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^