Main.cc: In function ‘void Sort()’: Main.cc:6:6: warning: unused variable ‘i’ [-Wunused-variable] int i,j; ^ Main.cc: In function ‘int main()’: Main.cc:24:7: error: no matching function for call to ‘sort()’ sort(); ^ In file included from /usr/include/c++/7/algorithm:62:0, from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:65, from Main.cc:1: /usr/include/c++/7/bits/stl_algo.h:4826:5: note: candidate: template void std::sort(_RAIter, _RAIter) sort(_RandomAccessIterator __first, _RandomAccessIterator __last) ^~~~ /usr/include/c++/7/bits/stl_algo.h:4826:5: note: template argument deduction/substitution failed: Main.cc:24:7: note: candidate expects 2 arguments, 0 provided sort(); ^ In file included from /usr/include/c++/7/algorithm:62:0, from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:65, from Main.cc:1: /usr/include/c++/7/bits/stl_algo.h:4856:5: note: candidate: template void std::sort(_RAIter, _RAIter, _Compare) sort(_RandomAccessIterator __first, _RandomAccessIterator __last, ^~~~ /usr/include/c++/7/bits/stl_algo.h:4856:5: note: template argument deduction/substitution failed: Main.cc:24:7: note: candidate expects 3 arguments, 0 provided sort(); ^