Compilare: user.cpp: In function ‘int main()’: user.cpp:43:13: warning: unused variable ‘plin2’ [-Wunused-variable] int plin2 = lower_bound(lin.begin(), lin.end(), u[i].i2) - lin.begin() + 1; ^ user.cpp:47:13: warning: unused variable ‘pcol2’ [-Wunused-variable] int pcol2 = lower_bound(col.begin(), col.end(), u[i].j2) - col.begin() + 1; ^ user.cpp:58:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1; i <= lin.size(); ++i) { ^ user.cpp:59:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 1; j <= col.size(); ++j) { ^