Apparently, I should have treated it normally, not as an error

du6/program.c

@@ -76,7 +76,7 @@ int main(void){
     
     if(!tree){
         printf("Bazu sa nedalo nacitat'.\n");
-        return 1;
+        return 0;
     }
     while( fgets(line, sizeof(line), stdin)){
          line[strcspn(line, "\n")] = '\0';
@@ -88,7 +88,7 @@ int main(void){
     }
     if(!whitespace){
         printf("No whitespace after database\n");
-        return 1;
+        return 0;
     }
     int numOfLeaves = count_leaves(tree);
     char answer[SIZE];
@@ -124,7 +124,7 @@ int main(void){
     }
     else{
         printf("\nNerozumiem\n");
-        return 1;
+        return 10;
     }
     }
     destroy_tree(tree);