Compilare: user.cpp: In function ‘int main()’: user.cpp:44:29: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] mat[i][++l]=NULL; ^ user.cpp:57:18: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] sir1[v[i]]=NULL; ^ user.cpp:58:45: warning: array subscript has type ‘char’ [-Wchar-subscripts] for(j=1;j<=v[i];j++)fr1[mat[i][j]]++; ^ user.cpp:71:37: warning: array subscript has type ‘char’ [-Wchar-subscripts] fr2[mat[lama][lama2]]++; ^ user.cpp:94:58: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] for(j=1;j<=v[u];j++)sir1[++l]=mat[vec[i]][j];sir1[++l]=NULL; ^