Compilare: user.cpp: In function ‘int main()’: user.cpp:131:45: warning: suggest parentheses around assignment used as truth value [-Wparentheses] for (int i = 1; i <= n; ++i) viz[i] = low[i] = lev[i] = 0; ^ user.cpp: In function ‘char nextch()’: user.cpp:27:56: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] if(pos==BUF_SIZE) fread(buf, BUF_SIZE, 1, f), pos=0; ^