Compilare: user.cpp: In function ‘int main()’: user.cpp:12:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<strlen(c);i++) ^ user.cpp:15:11: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if(c[i]>='0'&&c[i]<='9') ^