Compilare: user.cpp: In function ‘void back(int)’: user.cpp:20: warning: comparison between signed and unsigned integer expressions user.cpp:42: warning: comparison between signed and unsigned integer expressions user.cpp:41: warning: suggest explicit braces to avoid ambiguous ‘else’ user.cpp:51: warning: comparison between signed and unsigned integer expressions user.cpp:51: warning: suggest explicit braces to avoid ambiguous ‘else’ user.cpp: In function ‘int main()’: user.cpp:86: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void quick(int, int)’: user.cpp:106: warning: comparison between signed and unsigned integer expressions user.cpp:108: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘int valid(int)’: user.cpp:129: warning: comparison between signed and unsigned integer expressions