Compilare: user.cpp: In function ‘void make_prefix()’: user.cpp:11:11: warning: unused variable ‘n’ [-Wunused-variable] int k=0,n=0,m=t.size(); ^ user.cpp: At global scope: user.cpp:22:6: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] main(){ ^ user.cpp: In function ‘int main()’: user.cpp:33:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();i++){ ^