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:40:21: warning: array subscript has type 'char' [-Wchar-subscripts] node = node->child[ch]; ^ main.c: In function 'rm': main.c:53:21: warning: array subscript has type 'char' [-Wchar-subscripts] node = node->child[ch]; ^ main.c: In function 'query': main.c:76:18: warning: array subscript has type 'char' [-Wchar-subscripts] if (node->child[ch]) { ^ main.c:77:22: warning: array subscript has type 'char' [-Wchar-subscripts] node = node->child[ch]; ^ main.c: In function 'prefix': main.c:90:28: warning: array subscript has type 'char' [-Wchar-subscripts] if (ch < 0 || node->child[ch] == 0) ^ main.c:92:18: warning: array subscript has type 'char' [-Wchar-subscripts] if (node->child[ch]) { ^ main.c:93:22: warning: array subscript has type 'char' [-Wchar-subscripts] node = node->child[ch]; ^ main.c: In function 'main': main.c:115:17: warning: unused variable 'buf' [-Wunused-variable] char line[32], buf[32]; ^~~ main.c: In function 'rm': main.c:68:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ main.c: In function 'main': main.c:120:2: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen( "grader_test20.in", "r", stdin ); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:121:2: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen( "grader_test20.out", "w", stdout ); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:122:2: warning: ignoring return value of 'fgets', declared with attribute warn_unused_result [-Wunused-result]