Compilare: user.cpp: In function ‘int main()’: user.cpp:118:18: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] buf[m + 1] = NULL; ^~~~ user.cpp:70:31: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f, "%d%d ", &n, &m); ^ user.cpp: In function ‘char nextch()’: user.cpp:63:56: 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; ^