Compilare: user.cpp: In function ‘void cnt()’: user.cpp:17:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0,j=0,k;i<ss.size() && j<m*n;) { ^ user.cpp:18:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(k=i; k<ss.size() && ss[k].find(j)==ss[k].end(); ++k); ^ user.cpp:19:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(k==ss.size()) { ^ user.cpp:25:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(k=i+1; k<ss.size(); ++k) if(ss[k].find(j)!=ss[k].end()) { ^