Compilare: user.cpp: In function ‘int main()’: user.cpp:19:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0; i<strlen(a); i++) { ^ user.cpp:31:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0; i<strlen(a); i++) { ^ user.cpp:37:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=strlen(a); i<strlen(b); i++) { ^