Compilare: user.cpp: In function ‘long long int rez2(int, int)’: user.cpp:27:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<a[x][y].size();i++){ ^ user.cpp:33:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i<a[x][y].size()&&isalnum(a[x][y][i])){ ^ user.cpp:38:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(a[x][y][i]=='+'||i>=a[x][y].size()-1){ ^