Compilare: user.cpp: In function ‘bool substring(std::string, std::string)’: user.cpp:28:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k1==s1.length()) return 1; ^ user.cpp:13:9: warning: unused variable ‘i’ [-Wunused-variable] int i,j,k; ^ user.cpp:13:11: warning: unused variable ‘j’ [-Wunused-variable] int i,j,k; ^ user.cpp:13:13: warning: unused variable ‘k’ [-Wunused-variable] int i,j,k; ^ user.cpp:14:13: warning: unused variable ‘c2’ [-Wunused-variable] char c1,c2; ^ user.cpp:15:10: warning: unused variable ‘u’ [-Wunused-variable] bool u=false; ^ user.cpp: In function ‘int main()’: user.cpp:53:8: warning: unused variable ‘m’ [-Wunused-variable] int m=i; ^