Compilare: user.cpp: In function ‘bool isempty(char*)’: user.cpp:10:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<strlen(a);i++) ^ user.cpp: In function ‘int main()’: user.cpp:73:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<strlen(a);i++) ^ user.cpp:143:17: warning: ‘var’ may be used uninitialized in this function [-Wmaybe-uninitialized] for(;i<var;i++) ^