/in/foo.cc: In function 'int main()':
/in/foo.cc:54:4: warning: statement has no effect [-Wunused-value]
   l-1;
   ~^~
/in/foo.cc:32:10: warning: unused variable 'n1' [-Wunused-variable]
  int num,n1,n2,l,k,n;
          ^~
/in/foo.cc:47:4: warning: 'num' may be used uninitialized in this function [-Wmaybe-uninitialized]
    if(num>=k)
    ^~