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:40:21: warning: array subscript has type 'char' [-Wchar-subscripts] node = node->child[ch]; ^ main.c: In function 'query': main.c:65:18: warning: array subscript has type 'char' [-Wchar-subscripts] if (node->child[ch]) { ^ main.c:66:22: warning: array subscript has type 'char' [-Wchar-subscripts] node = node->child[ch]; ^ main.c: In function 'prefix': main.c:79:28: warning: array subscript has type 'char' [-Wchar-subscripts] if (ch < 0 || node->child[ch] == 0) ^ main.c:81:18: warning: array subscript has type 'char' [-Wchar-subscripts] if (node->child[ch]) { ^ main.c:82:22: warning: array subscript has type 'char' [-Wchar-subscripts] node = node->child[ch]; ^ main.c: In function 'main': main.c:93:5: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen( "trie.in", "r", stdin ); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:94:2: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen( "trie.out", "w", stdout ); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:97:2: warning: ignoring return value of 'fgets', declared with attribute warn_unused_result [-Wunused-result] fgets(line, 32, stdin); ^~~~~~~~~~~~~~~~~~~~~~ main.c:111:3: warning: ignoring return value of 'fgets', declared with attribute warn_unused_result [-Wunused-result] fgets(line, 32, stdin); ^~~~~~~~~~~~~~~~~~~~~~