Adding and updating values in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

How do you add a new key-value pair to a map in Go?

You add a new key-value pair by assigning a value to a new key like this: mapName[newKey] = newValue.

beginner

How do you update an existing value in a Go map?

You update a value by assigning a new value to an existing key: mapName[existingKey] = newValue.

beginner

What happens if you assign a value to a key that does not exist in a Go map?

Go will add the key to the map with the assigned value. Maps grow dynamically when you add new keys.

intermediate

Can you add or update values in a nil map in Go?

No, a nil map cannot be written to. You must initialize the map before adding or updating values.

beginner

Show a simple Go code snippet that adds and updates values in a map.

m := make(map[string]int)
m["apple"] = 5  // add
m["apple"] = 10 // update

What is the correct way to add a new key "banana" with value 3 to a map named fruits in Go?

A fruits["banana"] = 3

B fruits.add("banana", 3)

C fruits.insert("banana", 3)

D fruits.put("banana", 3)

In Go, you add or update map values by assigning: map[key] = value.

If you assign a value to an existing key in a Go map, what happens?

A The map is cleared

B A new key is added

C An error occurs

D The value for that key is updated

Assigning a value to an existing key updates that key's value.

What happens if you try to add a key-value pair to a nil map in Go?

A The map is automatically initialized

B The key-value pair is added successfully

C Runtime panic occurs

D The operation is ignored silently

Writing to a nil map causes a runtime panic. You must initialize the map first.

Which function is commonly used to initialize a map before adding values?

A make()

B new()

C init()

D create()

The make() function initializes maps, slices, and channels in Go.

How do you update the value of key "orange" to 7 in a map named fruits?

A fruits.update("orange", 7)

B fruits["orange"] = 7

C fruits.set("orange", 7)

D fruits.change("orange", 7)

Updating a map value is done by assigning a new value to the key.

Explain how to add and update values in a Go map. Include what happens if the key does not exist.

Think about how assignment works with maps.

What must you do before adding or updating values in a Go map to avoid runtime errors?

Consider what happens if the map is nil.