panic: assignment to entry in nil map

An "assignment to entry in nil map" error occurs in C++ when you try to assign a value to a key in a map that does not exist. Here's an explanation of each step leading to this error:

1. Declaring a map: You start by declaring a map variable using the syntax std::map<KeyType, ValueType> mapName;. This creates an empty map.

2. Accessing a non-existent key: Next, you try to access a key in the map that does not exist using the square bracket notation. For example, mapName[key] = value;. If the key doesn't exist, a new entry is created with the given key, and the assigned value is associated with it.

3. Assigning a value to a key: In this step, you attempt to assign a value to the key that you accessed in the previous step. However, if the key doesn't exist in the map, the "assignment to entry in nil map" error occurs.

To avoid this error, you need to ensure that the key you are trying to assign a value to already exists in the map. You can do this by checking if the key exists before assigning a value, using the count() or find() functions. Alternatively, you can use the insert() function to add a new key-value pair to the map.

Remember to handle this error gracefully in your code to prevent unexpected behavior or crashes.