Kotlin Ranges

Types of Ranges

val range = 1..5
// Contains: 1, 2, 3, 4, 5

val range = 1 until 5
// Contains: 1, 2, 3, 4

val range = 5 downTo 1
// Contains: 5, 4, 3, 2, 1

val range = 1..10 step 2
// Contains: 1, 3, 5, 7, 9

🔹 Creating Ranges

Different ways to create ranges:

fun main() {
    // Closed ranges (inclusive)
    val numbers = 1..10
    val letters = 'a'..'f'
    val floats = 1.0..5.0
    
    println("Closed ranges:")
    println("Numbers 1..10: ${numbers.toList()}")
    println("Letters 'a'..'f': ${letters.toList()}")
    
    // Open ranges (exclusive end)
    val openRange = 1 until 10
    println("\nOpen range 1 until 10: ${openRange.toList()}")
    
    // Reverse ranges
    val countdown = 10 downTo 1
    val reverseLetters = 'z' downTo 'u'
    
    println("\nReverse ranges:")
    println("Countdown 10 downTo 1: ${countdown.toList()}")
    println("Letters 'z' downTo 'u': ${reverseLetters.toList()}")
    
    // Step ranges
    val evens = 0..20 step 2
    val odds = 1..20 step 2
    
    println("\nStep ranges:")
    println("Even numbers 0..20 step 2: ${evens.toList()}")
    println("Odd numbers 1..20 step 2: ${odds.toList()}")
}

🔹 Using Ranges in Loops

Ranges are perfect for for loops:

fun main() {
    // Basic counting
    println("Counting 1 to 5:")
    for (i in 1..5) {
        print("$i ")
    }
    
    // Countdown
    println("\n\nCountdown from 5:")
    for (i in 5 downTo 1) {
        print("$i ")
    }
    println("🚀")
    
    // Skip counting
    println("\nEven numbers from 2 to 10:")
    for (i in 2..10 step 2) {
        print("$i ")
    }
    
    // Character ranges
    println("\n\nFirst 5 letters:")
    for (letter in 'A'..'E') {
        print("$letter ")
    }
    
    // Practical example: Creating a multiplication table
    println("\n\nMultiplication table for 3:")
    for (i in 1..10) {
        println("3 × $i = ${3 * i}")
    }
}

🔹 Checking if Values are in Range

Use 'in' operator to check membership:

fun main() {
    val validAges = 18..65
    val grades = 'A'..'F'
    val workingHours = 9..17
    
    // Check ages
    val ages = listOf(16, 25, 45, 70, 30)
    
    println("Age validation (valid range: 18-65):")
    for (age in ages) {
        if (age in validAges) {
            println("✅ Age $age: Valid for employment")
        } else {
            println("❌ Age $age: Outside valid range")
        }
    }
    
    // Check grades
    val studentGrades = listOf('A', 'B', 'X', 'C', 'Z')
    
    println("\nGrade validation (valid grades: A-F):")
    for (grade in studentGrades) {
        if (grade in grades) {
            println("✅ Grade '$grade': Valid")
        } else {
            println("❌ Grade '$grade': Invalid")
        }
    }
    
    // Check working hours
    val currentHour = 14 // 2 PM
    
    println("\nCurrent time: ${currentHour}:00")
    if (currentHour in workingHours) {
        println("✅ Office is open!")
    } else {
        println("❌ Office is closed!")
    }
}

🔹 Range Properties and Functions

Useful properties and methods:

fun main() {
    val range = 5..15
    val stepRange = 1..20 step 3
    val charRange = 'a'..'z'
    
    // Basic properties
    println("Range properties:")
    println("Range: $range")
    println("First: ${range.first}")
    println("Last: ${range.last}")
    println("Step: ${range.step}")
    
    // Check if empty
    val emptyRange = 10..5 // Invalid range
    println("\nEmpty range check:")
    println("Range 10..5 isEmpty: ${emptyRange.isEmpty()}")
    println("Range 5..15 isEmpty: ${range.isEmpty()}")
    
    // Convert to list
    println("\nConverting to collections:")
    println("Range as list: ${range.toList()}")
    println("Step range as list: ${stepRange.toList()}")
    println("First 5 letters: ${charRange.take(5).toList()}")
    
    // Random from range
    println("\nRandom values:")
    repeat(5) {
        println("Random from 1..100: ${(1..100).random()}")
    }
    
    // Contains check
    println("\nContains check:")
    println("Does 1..10 contain 5? ${5 in 1..10}")
    println("Does 1..10 contain 15? ${15 in 1..10}")
}

🔹 Practical Range Applications

Real-world examples using ranges:

fun main() {
    // Password strength checker
    fun checkPasswordStrength(password: String): String {
        val length = password.length
        
        return when {
            length in 1..5 -> "❌ Very Weak (too short)"
            length in 6..8 -> "⚠️ Weak"
            length in 9..12 -> "✅ Good"
            length in 13..20 -> "🔒 Strong"
            length > 20 -> "🛡️ Very Strong"
            else -> "❌ Invalid"
        }
    }
    
    // Test passwords
    val passwords = listOf("123", "password", "mySecretPass", "superSecurePassword123", "thisIsAnExtremelyLongPasswordThatIsVerySecure")
    
    println("Password Strength Analysis:")
    for (password in passwords) {
        val strength = checkPasswordStrength(password)
        println("'${password.take(10)}${if (password.length > 10) "..." else ""}' (${password.length} chars): $strength")
    }
    
    // Grade calculator
    fun calculateGrade(score: Int): String {
        return when (score) {
            in 90..100 -> "A (Excellent)"
            in 80..89 -> "B (Good)"
            in 70..79 -> "C (Average)"
            in 60..69 -> "D (Below Average)"
            in 0..59 -> "F (Fail)"
            else -> "Invalid Score"
        }
    }
    
    println("\nGrade Calculator:")
    val scores = listOf(95, 87, 76, 65, 45, 105)
    for (score in scores) {
        println("Score $score: ${calculateGrade(score)}")
    }
    
    // Age group classifier
    fun getAgeGroup(age: Int): String {
        return when (age) {
            in 0..2 -> "👶 Toddler"
            in 3..12 -> "🧒 Child"
            in 13..19 -> "👦 Teenager"
            in 20..39 -> "👨 Young Adult"
            in 40..59 -> "👨‍💼 Middle-aged"
            in 60..120 -> "👴 Senior"
            else -> "❓ Invalid Age"
        }
    }
    
    println("\nAge Group Classification:")
    val ages = listOf(2, 8, 16, 25, 45, 70)
    for (age in ages) {
        println("Age $age: ${getAgeGroup(age)}")
    }
}