Compilare: user.c: In function ‘hasAlphanumerical’: user.c:10:5: warning: implicit declaration of function ‘isalnum’ [-Wimplicit-function-declaration] if (isalnum(*s)) ^ user.c: In function ‘main’: user.c:34:5: warning: implicit declaration of function ‘strdup’ [-Wimplicit-function-declaration] keys[0] = strdup(""); ^ user.c:34:13: warning: assignment makes pointer from integer without a cast [enabled by default] keys[0] = strdup(""); ^ user.c:52:41: warning: assignment makes pointer from integer without a cast [enabled by default] keys[index / 2] = strdup(token); ^ user.c:58:43: warning: assignment makes pointer from integer without a cast [enabled by default] values[index / 2 - 1] = strdup(token); ^ user.c:29:12: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("convertor.in", "r", stdin); ^ user.c:30:12: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("convertor.out", "w", stdout); ^