Compilare: main.c: In function 'add': main.c:35:18: warning: array subscript has type 'char' [-Wchar-subscripts] if (node->child[ch] == NULL) { ^ main.c:36:18: warning: array subscript has type 'char' [-Wchar-subscripts] node->child[ch] = &mem[alloc_cnt++]; ^ main.c:37:18: warning: array subscript has type 'char' [-Wchar-subscripts] node->child[ch]->parent = node; ^ main.c:41:21: warning: array subscript has type 'char' [-Wchar-subscripts] node = node->child[ch]; ^ main.c: In function 'main': main.c:92:2: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen( "grader_test20.in", "r", stdin ); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:93:2: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen( "grader_test20.out", "w", stdout ); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:94:2: warning: ignoring return value of 'fgets', declared with attribute warn_unused_result [-Wunused-result] fgets(line, 32, stdin); ^~~~~~~~~~~~~~~~~~~~~~ main.c:108:3: warning: ignoring return value of 'fgets', declared with attribute warn_unused_result [-Wunused-result] fgets(line, 32, stdin); ^~~~~~~~~~~~~~~~~~~~~~