Array.contains() / firstIndex() / lastIndex()

// Checks whether the array contains the element.
array.contains(element)

// Checks whether the array contains an element matching the condition.
array.contains(where: { condition })

// Returns the index of the first element that matches the condition.
array.firstIndex(of: element)
array.firstIndex(where: { condition })

// Returns the index of the last element that matches the condition.
array.lastIndex(of: element)
array.lastIndex(where: { condition })

let scores = [78, 92, 55, 92, 61, 88]

// Check whether the array contains an element.
print(scores.contains(92))      // true
print(scores.contains(100))     // false

// Check whether the array contains an element matching a condition.
print(scores.contains(where: { $0 >= 90 })) // true (an element >= 90 exists)

// Search for the first matching index. The return value is optional.
if let index = scores.firstIndex(of: 92) {
    print(index) // 1 (index where 92 first appears)
}

// Search for the last matching index.
if let lastIdx = scores.lastIndex(of: 92) {
    print(lastIdx) // 3 (index where 92 last appears)
}

// Search for the first index satisfying a condition.
if let failIdx = scores.firstIndex(where: { $0 < 60 }) {
    print(failIdx)         // 2 (index where 55 first appears)
    print(scores[failIdx]) // 55
}

Use contains() to check for the presence of an element; it returns a Bool. You can pass a value directly as the argument if the element conforms to Equatable. For more complex conditions, use the where: variant.

The return values of firstIndex(of:) and lastIndex(of:) are Int? (optional). Because nil is returned when no element is found, always unwrap the result safely using optional binding (if let).

For adding and removing array elements, see append() / insert() / remove(). For filtering and sorting, see filter() / sorted().