Compilare: user.cpp: In function ‘void op()’: user.cpp:9:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<=strlen(s+1);i++) ^ user.cpp: In function ‘int main()’: user.cpp:18:10: warning: suggest parentheses around ‘+’ inside ‘>>’ [-Wparentheses] in>>s+1; ^