Compilare: main.cpp: In function 'int main()': main.cpp:22:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0;i < strlen(s);i++) ~~^~~~~~~~~~~ main.cpp:24:26: warning: NULL used in arithmetic [-Wpointer-arith] if ((isalpha(s[i]) == NULL)||(isdigit(s[i])==NULL)) ^~~~ main.cpp:24:49: warning: NULL used in arithmetic [-Wpointer-arith] if ((isalpha(s[i]) == NULL)||(isdigit(s[i])==NULL)) ^~~~ main.cpp:21:21: warning: ignoring return value of 'char* fgets(char*, int, FILE*)', declared with attribute warn_unused_result [-Wunused-result] fgets(s, 1024, in); ^