Maps and arrays are some of the most fundamental data structures. Reading and modifying their contents will be done often in any codebase.

Luckily, their properties grant them an easy-to-use syntax for looping through their elements. A programmer can use a tiny amount of code to manage large collections of data!

Each map and array has a set amount of items that they contain. In Go, the range keyword can be used to work through these items one at a time within a loop. For example:

letters := []string{"A", "B", "C", "D"}
for index, value := range letters {
  fmt.Println("Index:", index, "Value:", value)
}

Would output the following:

Index: 0 Value: A
Index: 1 Value: B
Index: 2 Value: C
Index: 3 Value: D

The range keyword is used here similarly to the initial statement of a definite loop. It lets the programmer assign two new variables for the index and value of each item in the array.

The behavior is the same for maps. But as they don’t have an index, range provides the key and value pairs for each item instead.

For example:

addressBook := map[string]string{
  "John": "12 Main St",
  "Janet": "56 Pleasant St",
  "Jordan": "88 Liberty Ln",
}
for key, value := range addressBook {
  fmt.Println("Name:", key, "Address:", value)
}

Which would output the following:

Name: John Address: 12 Main St
Name: Janet Address: 56 Pleasant St
Name: Jordan Address: 88 Liberty Ln

Now you can use loops for maps and arrays in Go!

Work through the following checkpoints to finish up the lesson!