Compilare: user.cpp: In function ‘int verif(int)’: user.cpp:31:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<strlen(x);++i) ^ user.cpp: In function ‘int main()’: user.cpp:47:9: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] x[0]=NULL; ^ user.cpp:53:27: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] x[strlen(x)-1]=NULL; ^ user.cpp:55:42: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] x[strlen(x)]=c,x[strlen(x)+1]=NULL; ^