Compilare: main.cpp: In function 'bool OK(int)': main.cpp:16:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(k==n) ~^~~ main.cpp: In function 'void back(unsigned int)': main.cpp:24:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=2 ; i<=n ; i++) ~^~~ main.cpp:27:3: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses] if( OK(k) ) ^