diff --git a/a.out b/a.out
new file mode 100755
index 0000000..0603d81
Binary files /dev/null and b/a.out differ
diff --git a/password_gen.c b/password_gen.c
index 22d3c20..0dfa54d 100644
--- a/password_gen.c
+++ b/password_gen.c
@@ -3,10 +3,17 @@
 #include <time.h>
 #include <string.h>
 
+#define error "minimal_length maximal_length options custom_characters\n"
+
 int str_to_int(char* str) {
   int output = 0;
 
   for (int i = 0; i < strlen(str); i++) {
+    if (str[i] < '0' || str[i] > '9') {
+      printf("That is not a number.\n");
+      exit(1);
+    }
+
     output *= 10;
     output += str[i] - '0';
   }
@@ -14,6 +21,13 @@ int str_to_int(char* str) {
   return output;
 }
 
+void not_avaliable_options(char** argv) {
+  if (strcmp(argv[3], "-c") != 0) {
+    printf(error);
+    exit(1);
+  }
+}
+
 void invalid_args(int argc) {
   if (argc < 4 && argc > 5) {
     printf("nuhuh\n");
@@ -37,7 +51,7 @@ char* character_list(int argc, char** argv) {
         case 'U':
           final_size += sizeof(uppercase) - 1;
           break;
-        case 'L':
+        case 'l':
           final_size += sizeof(lowercase) - 1;
           break;
         case 's':
@@ -46,42 +60,60 @@ char* character_list(int argc, char** argv) {
         case 'n':
           final_size += sizeof(numbers) - 1;
           break;
+        default:
+          printf(error);
+          exit(1);
       }
     }
+
     output = malloc(sizeof(char) * (final_size + 1));
 
-    int copy_index = 0;
+    int last_index = 0;
+    const char* current_list;
+    int size;
 
     for (int i = 0; argv[3][i] != '\0'; i++) {
-      const char* current_list;
-      int size;
-
       switch (argv[3][i]) {
         case 'U':
           current_list = uppercase;
-          size = sizeof(uppercase);
+          size = sizeof(uppercase) - 1;
           break;
-        case 'L':
+        case 'l':
           current_list = lowercase;
-          size = sizeof(lowercase);
+          size = sizeof(lowercase) - 1;
           break;
         case 's':
           current_list = symbols;
-          size = sizeof(symbols);
+          size = sizeof(symbols) - 1;
           break;
         case 'n':
           current_list = numbers;
-          size = sizeof(numbers);
+          size = sizeof(numbers) - 1;
           break;
       }
 
-      for (int j = 0; j < size - 1; j++) {
-        output[copy_index] = current_list[j];
-        copy_index++;
+      for (int j = 0; j < size; j++) {
+        output[last_index] = current_list[j];
+        last_index++;
       }
-
-      output[final_size] = '\0';
     }
+    output[final_size] = '\0';
+  }
+
+  else if (argc == 5) {
+    int final_size = 0;
+
+    for (int i = 0; argv[4][i] != '\0'; i++) {
+      final_size++;
+    }
+
+    output = malloc(sizeof(char) * (final_size + 1));
+
+    for (int i = 0; argv[4][i] != '\0'; i++) {
+      output[i] = argv[4][i];
+    }
+
+    output[final_size] = '\0';
   }
 
   return output;
@@ -106,16 +138,26 @@ char* random_str(int length, char* symbols) {
 
 int main(int argc, char** argv) {
   invalid_args(argc);
+
+  if (argc == 5) {
+    not_avaliable_options(argv);
+  }
+
   srand(time(NULL));
 
   int min_length = str_to_int(argv[1]);
   int max_length = str_to_int(argv[2]);
 
+  if (min_length > max_length) {
+    printf("Your minimal length is longer than your maximal length.\n");
+    exit(1);
+  }
+
   int length = random_len(min_length, max_length);
 
-  if (argc == 4) {
-    char* password = random_str(length, character_list(argc, argv));
-    puts(password);
-    free(password);
-  }
+  char* symbols = character_list(argc, argv);
+  char* password = random_str(length, symbols);
+  free(symbols);
+  puts(password);
+  free(password);
 }