# Assignment

The binary assignment operator `=` can be used to assign a new value to a variable. It is only allowed in a statement and is not allowed in expressions.

```
var a = 1
a = 2
// `a` is `2`


var b = 3
var c = 4

// Invalid: The assignment operation cannot be used in an expression.
a = b = c

// Instead, the intended assignment must be written in multiple statements.
b = c
a = b
```

Assignments to constants are invalid.

```
let a = 1
// Invalid: Assignments are only for variables, not constants.
a = 2
```

The left-hand side of the assignment operand must be an identifier. For arrays and dictionaries, this identifier can be followed by one or more index or access expressions.

```
// Declare an array of integers.
let numbers = [1, 2]

// Change the first element of the array.
//
numbers[0] = 3

// `numbers` is `[3, 2]`
```

```
// Declare an array of arrays of integers.
let arrays = [[1, 2], [3, 4]]

// Change the first element in the second array
//
arrays[1][0] = 5

// `arrays` is `[[1, 2], [5, 4]]`
```

```
let dictionaries = {
  true: {1: 2},
  false: {3: 4}
}

dictionaries[false][3] = 0

// `dictionaries` is `{
//   true: {1: 2},
//   false: {3: 0}
//}`
```


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