Compilare: user.cpp: In function ‘int main()’: user.cpp:26:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<strlen(a);i++) ^ user.cpp:57:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<strlen(a);i++) ^ user.cpp:62:23: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] b[strlen(a)+2]=NULL; ^ user.cpp:64:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<strlen(a)-2;i++) ^ user.cpp:12:24: warning: unused variable ‘c’ [-Wunused-variable] char a[255],b[257],c[4]; ^