diff --git a/README.md b/README.md
index 08d4aa4..e9214d0 100644
--- a/README.md
+++ b/README.md
@@ -1,10 +1,47 @@
-Kalkulator BMI
-===============
+# BMI Calculator Android App
 
-Silahkan kembangkan aplikasi ini untuk melakukan perhitungan BMI
+**NPM**: 202310715043  
+**Nama**: Muhammad Rafly Al Fathir
 
-Petunjuk lebih detil dapat dibaca di
-https://docs.google.com/document/d/1iGiC0Bg3Bdcd2Maq45TYkCDUkZ5Ql51E/edit?rtpof=true
+## Deskripsi
+Aplikasi Android untuk menghitung Body Mass Index (BMI) berdasarkan tinggi dan berat badan. Aplikasi ini mendukung dua sistem unit: Metrik (cm, kg) dan US Customary (inches, lbs).
 
-Starter dimodifikasi dan terinspirasi dari:
-https://developer.android.com/codelabs/basic-android-compose-calculate-tip#0
\ No newline at end of file
+## Fitur
+- ✅ Perhitungan BMI yang akurat
+- ✅ Dukungan untuk sistem Metrik dan USC
+- ✅ Validasi input untuk mencegah nilai yang tidak wajar
+- ✅ Kategori BMI (Underweight, Normal, Overweight, Obese)
+- ✅ UI modern dengan Material Design 3
+- ✅ Color coding untuk kategori BMI
+- ✅ Informasi lengkap tentang kategori BMI
+
+## Teknologi yang Digunakan
+- **Kotlin**: Bahasa pemrograman utama
+- **Jetpack Compose**: UI Framework
+- **Material Design 3**: Design system
+- **JUnit**: Unit testing
+
+## Formula BMI
+```
+BMI = Berat (kg) / (Tinggi (m))²
+```
+
+## Kategori BMI (WHO)
+- **Underweight**: BMI < 18.5
+- **Normal**: 18.5 ≤ BMI < 25
+- **Overweight**: 25 ≤ BMI < 30
+- **Obese**: BMI ≥ 30
+
+## Unit Testing
+Aplikasi dilengkapi dengan unit test untuk:
+- Perhitungan BMI (sistem metrik dan USC)
+- Kategori BMI
+- Validasi input
+- Boundary cases
+
+## Kontribusi & Kredit
+Aplikasi ini dikembangkan dengan bantuan Claude ai dalam pembuatan kode, desain antarmuka, dan dokumentasi.
+
+
+## Lisensi
+Apache License 2.0
\ No newline at end of file
diff --git a/app/src/main/java/com/example/tiptime/MainActivity.kt b/app/src/main/java/com/example/tiptime/MainActivity.kt
index d0fdd80..64d1c12 100644
--- a/app/src/main/java/com/example/tiptime/MainActivity.kt
+++ b/app/src/main/java/com/example/tiptime/MainActivity.kt
@@ -17,10 +17,10 @@ package com.example.tiptime
 
 import android.os.Bundle
 import androidx.activity.ComponentActivity
+import androidx.activity.compose.BackHandler
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
 import androidx.annotation.DrawableRes
-import androidx.annotation.StringRes
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
@@ -30,17 +30,28 @@ import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.safeDrawingPadding
-import androidx.compose.foundation.layout.statusBarsPadding
-import androidx.compose.foundation.layout.wrapContentWidth
+import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.text.KeyboardOptions
 import androidx.compose.foundation.verticalScroll
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material3.Button
+import androidx.compose.material3.ButtonDefaults
+import androidx.compose.material3.Card
+import androidx.compose.material3.CardDefaults
+import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Surface
 import androidx.compose.material3.Switch
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextField
+import androidx.compose.material3.TextFieldDefaults
+import androidx.compose.material3.TopAppBar
+import androidx.compose.material3.TopAppBarDefaults
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
@@ -48,14 +59,15 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.res.painterResource
-import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.input.ImeAction
 import androidx.compose.ui.text.input.KeyboardType
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
 import com.example.tiptime.ui.theme.TipTimeTheme
-import java.text.NumberFormat
+import kotlin.math.pow
 
 class MainActivity : ComponentActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
@@ -66,82 +78,294 @@ class MainActivity : ComponentActivity() {
                 Surface(
                     modifier = Modifier.fillMaxSize(),
                 ) {
-                    TipTimeLayout()
+                    // State untuk menentukan halaman mana yang ditampilkan
+                    var showWelcomeScreen by remember { mutableStateOf(true) }
+
+                    if (showWelcomeScreen) {
+                        // Tampilkan Welcome Screen
+                        WelcomeScreen(
+                            onStartClick = {
+                                showWelcomeScreen = false // Pindah ke halaman BMI Calculator
+                            }
+                        )
+                    } else {
+                        // Tampilkan BMI Calculator dengan tombol back
+                        BMICalculatorLayout(
+                            onBackClick = {
+                                showWelcomeScreen = true // Kembali ke Welcome Screen
+                            }
+                        )
+                    }
                 }
             }
         }
     }
 }
 
+/**
+ * Layout utama untuk aplikasi BMI Calculator
+ * Menampilkan input field untuk tinggi dan berat badan,
+ * toggle untuk unit sistem, dan hasil perhitungan BMI
+ *
+ * @param onBackClick Callback yang dipanggil ketika tombol back diklik
+ */
+@OptIn(ExperimentalMaterial3Api::class)
 @Composable
-fun TipTimeLayout() {
-    var amountInput by remember { mutableStateOf("") }
-    var tipInput by remember { mutableStateOf("") }
-    var roundUp by remember { mutableStateOf(false) }
+fun BMICalculatorLayout(onBackClick: () -> Unit = {}) {
+    var heightInput by remember { mutableStateOf("") }
+    var weightInput by remember { mutableStateOf("") }
+    var useUSC by remember { mutableStateOf(false) }
 
-    val BmiHeight = amountInput.toDoubleOrNull() ?: 0.0
-    val BmiWeight = tipInput.toDoubleOrNull() ?: 0.0
-    val bmi = calculateBMI(BmiHeight, BmiWeight, roundUp)
-    val category = calculateBMICategory(BmiHeight, BmiWeight, roundUp)
+    // Konversi input ke Double atau null jika tidak valid
+    val height = heightInput.toDoubleOrNull() ?: 0.0
+    val weight = weightInput.toDoubleOrNull() ?: 0.0
 
-    Column(
-        modifier = Modifier
-            .statusBarsPadding()
-            .padding(horizontal = 40.dp)
-            .verticalScroll(rememberScrollState())
-            .safeDrawingPadding(),
-        horizontalAlignment = Alignment.CenterHorizontally,
-        verticalArrangement = Arrangement.Center
-    ) {
-        Text(
-            text = stringResource(R.string.calculate_tip),
+    // Validasi input
+    val inputError = validateInput(height, weight, useUSC)
+
+    // Hitung BMI dan kategori jika input valid
+    val bmi = if (inputError == null) {
+        calculateBMI(height, weight, useUSC)
+    } else {
+        0.0
+    }
+
+    val category = if (inputError == null && bmi > 0) {
+        calculateBMICategory(bmi)
+    } else {
+        ""
+    }
+
+    val categoryColor = getBMICategoryColor(category)
+
+    // Gunakan Scaffold untuk layout dengan TopAppBar
+    Scaffold(
+        topBar = {
+            TopAppBar(
+                title = {
+                    Text(
+                        text = "BMI Calculator",
+                        fontWeight = FontWeight.Bold
+                    )
+                },
+                navigationIcon = {
+                    IconButton(onClick = onBackClick) {
+                        Icon(
+                            imageVector = Icons.AutoMirrored.Filled.ArrowBack,
+                            contentDescription = "Back to Welcome Screen",
+                            modifier = Modifier.size(24.dp)
+                        )
+                    }
+                },
+                colors = TopAppBarDefaults.topAppBarColors(
+                    containerColor = MaterialTheme.colorScheme.primaryContainer,
+                    titleContentColor = MaterialTheme.colorScheme.onPrimaryContainer,
+                    navigationIconContentColor = MaterialTheme.colorScheme.onPrimaryContainer
+                )
+            )
+        }
+    ) { paddingValues ->
+        Column(
             modifier = Modifier
-                .padding(bottom = 16.dp, top = 40.dp)
-                .align(alignment = Alignment.Start)
-        )
-        EditNumberField(
-            label = R.string.height,
-            leadingIcon = R.drawable.number,
-            keyboardOptions = KeyboardOptions.Default.copy(
-                keyboardType = KeyboardType.Number,
-                imeAction = ImeAction.Next
-            ),
-            value = amountInput,
-            onValueChanged = { amountInput = it },
-            modifier = Modifier.padding(bottom = 32.dp).fillMaxWidth(),
-        )
-        EditNumberField(
-            label = R.string.weight,
-            leadingIcon = R.drawable.number,
-            keyboardOptions = KeyboardOptions.Default.copy(
-                keyboardType = KeyboardType.Number,
-                imeAction = ImeAction.Done
-            ),
-            value = tipInput,
-            onValueChanged = { tipInput = it },
-            modifier = Modifier.padding(bottom = 32.dp).fillMaxWidth(),
-        )
-        RoundTheTipRow(
-            roundUp = roundUp,
-            onRoundUpChanged = { roundUp = it },
-            modifier = Modifier.padding(bottom = 32.dp)
-        )
-        Text(
-            text = stringResource(R.string.bmi_calculation, bmi),
-            style = MaterialTheme.typography.displaySmall
-        )
-        Text(
-            text = stringResource(R.string.bmi_category, category),
-            style = MaterialTheme.typography.displaySmall
-        )
+                .fillMaxSize()
+                .padding(paddingValues)
+                .padding(horizontal = 24.dp)
+                .verticalScroll(rememberScrollState())
+                .safeDrawingPadding(),
+            horizontalAlignment = Alignment.CenterHorizontally,
+            verticalArrangement = Arrangement.Top
+        ) {
+            Spacer(modifier = Modifier.height(16.dp))
 
-        Spacer(modifier = Modifier.height(150.dp))
+            // Subtitle
+            Text(
+                text = "Calculate your Body Mass Index",
+                style = MaterialTheme.typography.bodyMedium,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                modifier = Modifier
+                    .padding(bottom = 24.dp)
+                    .align(alignment = Alignment.Start)
+            )
+
+            // Input Field untuk Tinggi
+            EditNumberField(
+                label = if (useUSC) "Height (inches)" else "Height (cm)",
+                leadingIcon = R.drawable.number,
+                keyboardOptions = KeyboardOptions.Default.copy(
+                    keyboardType = KeyboardType.Decimal,
+                    imeAction = ImeAction.Next
+                ),
+                value = heightInput,
+                onValueChanged = { heightInput = it },
+                modifier = Modifier
+                    .padding(bottom = 16.dp)
+                    .fillMaxWidth(),
+            )
+
+            // Input Field untuk Berat
+            EditNumberField(
+                label = if (useUSC) "Weight (lbs)" else "Weight (kg)",
+                leadingIcon = R.drawable.number,
+                keyboardOptions = KeyboardOptions.Default.copy(
+                    keyboardType = KeyboardType.Decimal,
+                    imeAction = ImeAction.Done
+                ),
+                value = weightInput,
+                onValueChanged = { weightInput = it },
+                modifier = Modifier
+                    .padding(bottom = 16.dp)
+                    .fillMaxWidth(),
+            )
+
+            // Toggle untuk Unit Sistem
+            UnitSystemToggleRow(
+                useUSC = useUSC,
+                onToggleChanged = { useUSC = it },
+                modifier = Modifier.padding(bottom = 24.dp)
+            )
+
+            // Tampilkan error jika ada
+            if (inputError != null) {
+                Card(
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .padding(bottom = 16.dp),
+                    colors = CardDefaults.cardColors(
+                        containerColor = MaterialTheme.colorScheme.errorContainer
+                    )
+                ) {
+                    Text(
+                        text = inputError,
+                        color = MaterialTheme.colorScheme.onErrorContainer,
+                        modifier = Modifier.padding(16.dp),
+                        style = MaterialTheme.typography.bodyMedium
+                    )
+                }
+            }
+
+            // Tampilkan hasil BMI jika valid
+            if (inputError == null && bmi > 0) {
+                Card(
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .padding(bottom = 16.dp),
+                    colors = CardDefaults.cardColors(
+                        containerColor = MaterialTheme.colorScheme.primaryContainer
+                    )
+                ) {
+                    Column(
+                        modifier = Modifier.padding(24.dp),
+                        horizontalAlignment = Alignment.CenterHorizontally
+                    ) {
+                        Text(
+                            text = "Your BMI",
+                            style = MaterialTheme.typography.titleMedium,
+                            color = MaterialTheme.colorScheme.onPrimaryContainer
+                        )
+
+                        Text(
+                            text = String.format("%.1f", bmi),
+                            style = MaterialTheme.typography.displayLarge,
+                            fontWeight = FontWeight.Bold,
+                            color = MaterialTheme.colorScheme.primary,
+                            modifier = Modifier.padding(vertical = 8.dp)
+                        )
+
+                        if (category.isNotEmpty()) {
+                            Card(
+                                colors = CardDefaults.cardColors(
+                                    containerColor = categoryColor
+                                )
+                            ) {
+                                Text(
+                                    text = category,
+                                    style = MaterialTheme.typography.titleLarge,
+                                    fontWeight = FontWeight.Bold,
+                                    color = Color.White,
+                                    modifier = Modifier.padding(horizontal = 16.dp, vertical = 8.dp)
+                                )
+                            }
+                        }
+                    }
+                }
+
+                // Informasi Kategori BMI
+                BMICategoryInfo()
+            }
+
+            Spacer(modifier = Modifier.height(40.dp))
+        }
     }
 }
 
+/**
+ * Composable untuk menampilkan informasi kategori BMI
+ */
+@Composable
+fun BMICategoryInfo() {
+    Card(
+        modifier = Modifier
+            .fillMaxWidth()
+            .padding(bottom = 16.dp),
+        colors = CardDefaults.cardColors(
+            containerColor = MaterialTheme.colorScheme.surfaceVariant
+        )
+    ) {
+        Column(
+            modifier = Modifier.padding(16.dp)
+        ) {
+            Text(
+                text = "BMI Categories",
+                style = MaterialTheme.typography.titleMedium,
+                fontWeight = FontWeight.Bold,
+                modifier = Modifier.padding(bottom = 8.dp)
+            )
+
+            BMICategoryItem("Underweight", "< 18.5", Color(0xFF2196F3))
+            BMICategoryItem("Normal", "18.5 - 24.9", Color(0xFF4CAF50))
+            BMICategoryItem("Overweight", "25.0 - 29.9", Color(0xFFFFA726))
+            BMICategoryItem("Obese", "≥ 30.0", Color(0xFFF44336))
+        }
+    }
+}
+
+/**
+ * Composable untuk menampilkan satu item kategori BMI
+ */
+@Composable
+fun BMICategoryItem(category: String, range: String, color: Color) {
+    Row(
+        modifier = Modifier
+            .fillMaxWidth()
+            .padding(vertical = 4.dp),
+        horizontalArrangement = Arrangement.SpaceBetween,
+        verticalAlignment = Alignment.CenterVertically
+    ) {
+        Row(verticalAlignment = Alignment.CenterVertically) {
+            Card(
+                modifier = Modifier.padding(end = 8.dp),
+                colors = CardDefaults.cardColors(containerColor = color)
+            ) {
+                Spacer(modifier = Modifier
+                    .height(16.dp)
+                    .padding(horizontal = 8.dp))
+            }
+            Text(text = category, style = MaterialTheme.typography.bodyMedium)
+        }
+        Text(
+            text = range,
+            style = MaterialTheme.typography.bodyMedium,
+            fontWeight = FontWeight.Bold
+        )
+    }
+}
+
+/**
+ * Composable untuk input field angka dengan label dan icon
+ */
 @Composable
 fun EditNumberField(
-    @StringRes label: Int,
+    label: String,
     @DrawableRes leadingIcon: Int,
     keyboardOptions: KeyboardOptions,
     value: String,
@@ -151,64 +375,163 @@ fun EditNumberField(
     TextField(
         value = value,
         singleLine = true,
-        leadingIcon = { Icon(painter = painterResource(id = leadingIcon), null) },
+        leadingIcon = {
+            Icon(
+                painter = painterResource(id = leadingIcon),
+                contentDescription = null,
+                tint = MaterialTheme.colorScheme.primary
+            )
+        },
         modifier = modifier,
         onValueChange = onValueChanged,
-        label = { Text(stringResource(label)) },
-        keyboardOptions = keyboardOptions
+        label = { Text(label) },
+        keyboardOptions = keyboardOptions,
+        colors = TextFieldDefaults.colors(
+            focusedContainerColor = MaterialTheme.colorScheme.surface,
+            unfocusedContainerColor = MaterialTheme.colorScheme.surface,
+        )
     )
 }
 
+/**
+ * Composable untuk row toggle unit sistem (Metrik/USC)
+ */
 @Composable
-fun RoundTheTipRow(
-    roundUp: Boolean,
-    onRoundUpChanged: (Boolean) -> Unit,
+fun UnitSystemToggleRow(
+    useUSC: Boolean,
+    onToggleChanged: (Boolean) -> Unit,
     modifier: Modifier = Modifier
 ) {
     Row(
         modifier = modifier.fillMaxWidth(),
-        verticalAlignment = Alignment.CenterVertically
+        verticalAlignment = Alignment.CenterVertically,
+        horizontalArrangement = Arrangement.SpaceBetween
     ) {
-        Text(text = stringResource(R.string.use_usc))
+        Column {
+            Text(
+                text = "Unit System",
+                style = MaterialTheme.typography.titleMedium,
+                fontWeight = FontWeight.Bold
+            )
+            Text(
+                text = if (useUSC) "US Customary (in, lbs)" else "Metric (cm, kg)",
+                style = MaterialTheme.typography.bodySmall,
+                color = MaterialTheme.colorScheme.onSurfaceVariant
+            )
+        }
         Switch(
-            modifier = Modifier
-                .fillMaxWidth()
-                .wrapContentWidth(Alignment.End),
-            checked = roundUp,
-            onCheckedChange = onRoundUpChanged
+            checked = useUSC,
+            onCheckedChange = onToggleChanged
         )
     }
 }
 
 /**
- * Calculates the BMI
+ * Validasi input tinggi dan berat badan
  *
- * Catatan: tambahkan unit test untuk kalkulasi BMI ini
+ * @param height Tinggi badan dalam cm atau inches
+ * @param weight Berat badan dalam kg atau lbs
+ * @param useUSC True jika menggunakan unit USC, false untuk metrik
+ * @return String error message jika tidak valid, null jika valid
  */
-private fun calculateBMI(BmiHeight: Double, BmiWeight: Double = 15.0, roundUp: Boolean): String {
-    var bmi = BmiWeight / 100 * BmiHeight
-    if (roundUp) {
-        bmi = kotlin.math.ceil(bmi)
+fun validateInput(height: Double, weight: Double, useUSC: Boolean): String? {
+    if (height <= 0 || weight <= 0) {
+        return "Please enter valid height and weight"
     }
-    return NumberFormat.getNumberInstance().format(bmi)
-}
-/**
- * Calculates the BMI Category
- *
- * Catatan: tambahkan unit test untuk kalkulasi BMI ini
- */
 
-private fun calculateBMICategory(BmiHeight: Double, BmiWeight: Double = 15.0, roundUp: Boolean): String {
-    var bmi = BmiWeight / 100 * BmiHeight
-    if (roundUp) {
-        bmi = kotlin.math.ceil(bmi)
+    // Validasi untuk sistem metrik (cm, kg)
+    if (!useUSC) {
+        if (height < 50 || height > 300) {
+            return "Height must be between 50-300 cm"
+        }
+        if (weight < 10 || weight > 500) {
+            return "Weight must be between 10-500 kg"
+        }
     }
-    return NumberFormat.getNumberInstance().format(bmi)
+    // Validasi untuk sistem USC (inches, lbs)
+    else {
+        if (height < 20 || height > 120) {
+            return "Height must be between 20-120 inches"
+        }
+        if (weight < 20 || weight > 1100) {
+            return "Weight must be between 20-1100 lbs"
+        }
+    }
+
+    return null
 }
+
+/**
+ * Menghitung BMI (Body Mass Index)
+ *
+ * Formula BMI: weight (kg) / (height (m))^2
+ *
+ * @param height Tinggi badan dalam cm (metrik) atau inches (USC)
+ * @param weight Berat badan dalam kg (metrik) atau lbs (USC)
+ * @param useUSC True jika menggunakan unit USC, false untuk metrik
+ * @return Nilai BMI
+ */
+fun calculateBMI(height: Double, weight: Double, useUSC: Boolean): Double {
+    if (height <= 0 || weight <= 0) return 0.0
+
+    val heightInMeters: Double
+    val weightInKg: Double
+
+    if (useUSC) {
+        // Konversi dari inches ke meter dan lbs ke kg
+        heightInMeters = height * 0.0254
+        weightInKg = weight * 0.453592
+    } else {
+        // Konversi dari cm ke meter
+        heightInMeters = height / 100.0
+        weightInKg = weight
+    }
+
+    // Formula BMI: weight / height^2
+    return weightInKg / heightInMeters.pow(2)
+}
+
+/**
+ * Menentukan kategori BMI berdasarkan nilai BMI
+ *
+ * Kategori WHO:
+ * - Underweight: BMI < 18.5
+ * - Normal weight: 18.5 ≤ BMI < 25
+ * - Overweight: 25 ≤ BMI < 30
+ * - Obese: BMI ≥ 30
+ *
+ * @param bmi Nilai BMI
+ * @return Kategori BMI dalam bentuk String
+ */
+fun calculateBMICategory(bmi: Double): String {
+    return when {
+        bmi < 18.5 -> "Underweight"
+        bmi < 25.0 -> "Normal"
+        bmi < 30.0 -> "Overweight"
+        else -> "Obese"
+    }
+}
+
+/**
+ * Mendapatkan warna untuk kategori BMI
+ *
+ * @param category Kategori BMI
+ * @return Color yang sesuai dengan kategori
+ */
+fun getBMICategoryColor(category: String): Color {
+    return when (category) {
+        "Underweight" -> Color(0xFF2196F3) // Blue
+        "Normal" -> Color(0xFF4CAF50) // Green
+        "Overweight" -> Color(0xFFFFA726) // Orange
+        "Obese" -> Color(0xFFF44336) // Red
+        else -> Color.Gray
+    }
+}
+
 @Preview(showBackground = true)
 @Composable
-fun TipTimeLayoutPreview() {
+fun BMICalculatorLayoutPreview() {
     TipTimeTheme {
-        TipTimeLayout()
+        BMICalculatorLayout()
     }
 }
\ No newline at end of file
diff --git a/app/src/main/java/com/example/tiptime/WelcomeScreen.kt b/app/src/main/java/com/example/tiptime/WelcomeScreen.kt
new file mode 100644
index 0000000..e431919
--- /dev/null
+++ b/app/src/main/java/com/example/tiptime/WelcomeScreen.kt
@@ -0,0 +1,236 @@
+package com.example.tiptime
+
+import androidx.compose.animation.core.Animatable
+import androidx.compose.animation.core.tween
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material3.Button
+import androidx.compose.material3.ButtonDefaults
+import androidx.compose.material3.Card
+import androidx.compose.material3.CardDefaults
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.remember
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.scale
+import androidx.compose.ui.res.painterResource
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.tooling.preview.Preview
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import com.example.tiptime.ui.theme.TipTimeTheme
+
+/**
+ * Composable untuk halaman Welcome Screen
+ *
+ * @param onStartClick Callback yang dipanggil ketika tombol "MULAI" diklik
+ */
+@Composable
+fun WelcomeScreen(onStartClick: () -> Unit) {
+    // Animasi scale untuk efek zoom-in saat halaman muncul
+    val scale = remember { Animatable(0.8f) }
+
+    // Jalankan animasi saat composable pertama kali ditampilkan
+    LaunchedEffect(Unit) {
+        scale.animateTo(
+            targetValue = 1f,
+            animationSpec = tween(durationMillis = 800)
+        )
+    }
+
+    // Background dengan warna theme
+    Box(
+        modifier = Modifier
+            .fillMaxSize()
+            .background(MaterialTheme.colorScheme.background),
+        contentAlignment = Alignment.Center
+    ) {
+        Column(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(32.dp)
+                .scale(scale.value),
+            horizontalAlignment = Alignment.CenterHorizontally,
+            verticalArrangement = Arrangement.Center
+        ) {
+            // Icon/Logo Aplikasi
+            Card(
+                modifier = Modifier
+                    .size(120.dp)
+                    .padding(bottom = 24.dp),
+                shape = RoundedCornerShape(60.dp),
+                colors = CardDefaults.cardColors(
+                    containerColor = MaterialTheme.colorScheme.primaryContainer
+                ),
+                elevation = CardDefaults.cardElevation(defaultElevation = 8.dp)
+            ) {
+                Box(
+                    modifier = Modifier.fillMaxSize(),
+                    contentAlignment = Alignment.Center
+                ) {
+                    Icon(
+                        painter = painterResource(id = R.drawable.number),
+                        contentDescription = "BMI Calculator Icon",
+                        modifier = Modifier.size(64.dp),
+                        tint = MaterialTheme.colorScheme.primary
+                    )
+                }
+            }
+
+            // Judul Aplikasi
+            Text(
+                text = "BMI Calculator",
+                fontSize = 36.sp,
+                fontWeight = FontWeight.Bold,
+                color = MaterialTheme.colorScheme.primary,
+                textAlign = TextAlign.Center
+            )
+
+            Text(
+                text = "Body Mass Index Calculator",
+                fontSize = 16.sp,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                textAlign = TextAlign.Center,
+                modifier = Modifier.padding(top = 8.dp, bottom = 32.dp)
+            )
+
+            // Card Biodata Pengembang
+            Card(
+                modifier = Modifier
+                    .fillMaxWidth()
+                    .padding(bottom = 32.dp),
+                shape = RoundedCornerShape(20.dp),
+                colors = CardDefaults.cardColors(
+                    containerColor = MaterialTheme.colorScheme.surface
+                ),
+                elevation = CardDefaults.cardElevation(defaultElevation = 4.dp)
+            ) {
+                Column(
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .padding(24.dp),
+                    horizontalAlignment = Alignment.CenterHorizontally
+                ) {
+                    Text(
+                        text = "👨‍💻 Dikembangkan Oleh",
+                        fontSize = 14.sp,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant,
+                        textAlign = TextAlign.Center,
+                        modifier = Modifier.padding(bottom = 16.dp)
+                    )
+
+                    // NPM
+                    InfoRow(
+                        label = "NPM",
+                        value = "202310715043"
+                    )
+
+                    Spacer(modifier = Modifier.height(12.dp))
+
+                    // Nama
+                    InfoRow(
+                        label = "Nama",
+                        value = "M Rafly Al Fathir"
+                    )
+
+                    Spacer(modifier = Modifier.height(12.dp))
+
+                    // Program Studi (opsional)
+                    InfoRow(
+                        label = "Prodi",
+                        value = "Teknik Informatika"
+                    )
+                }
+            }
+
+            // Deskripsi Singkat
+            Text(
+                text = "Aplikasi untuk menghitung Body Mass Index (BMI) berdasarkan tinggi dan berat badan Anda dengan dukungan sistem Metrik dan US Customary.",
+                fontSize = 14.sp,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                textAlign = TextAlign.Center,
+                modifier = Modifier.padding(bottom = 32.dp)
+            )
+
+            // Tombol MULAI
+            Button(
+                onClick = onStartClick,
+                modifier = Modifier
+                    .fillMaxWidth()
+                    .height(56.dp),
+                shape = RoundedCornerShape(16.dp),
+                colors = ButtonDefaults.buttonColors(
+                    containerColor = MaterialTheme.colorScheme.primary,
+                    contentColor = MaterialTheme.colorScheme.onPrimary
+                ),
+                elevation = ButtonDefaults.buttonElevation(
+                    defaultElevation = 4.dp,
+                    pressedElevation = 8.dp
+                )
+            ) {
+                Text(
+                    text = "MULAI",
+                    fontSize = 18.sp,
+                    fontWeight = FontWeight.Bold,
+                    letterSpacing = 1.2.sp
+                )
+            }
+
+            Spacer(modifier = Modifier.height(16.dp))
+
+            // Copyright
+            Text(
+                text = "© 2024 BMI Calculator App",
+                fontSize = 12.sp,
+                color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.7f),
+                textAlign = TextAlign.Center
+            )
+        }
+    }
+}
+
+/**
+ * Composable untuk menampilkan baris informasi (label: value)
+ */
+@Composable
+fun InfoRow(label: String, value: String) {
+    Column(
+        horizontalAlignment = Alignment.CenterHorizontally
+    ) {
+        Text(
+            text = label,
+            fontSize = 12.sp,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+            fontWeight = FontWeight.Medium
+        )
+        Text(
+            text = value,
+            fontSize = 18.sp,
+            color = MaterialTheme.colorScheme.onSurface,
+            fontWeight = FontWeight.Bold,
+            modifier = Modifier.padding(top = 4.dp)
+        )
+    }
+}
+
+@Preview(showBackground = true)
+@Composable
+fun WelcomeScreenPreview() {
+    TipTimeTheme {
+        WelcomeScreen(onStartClick = {})
+    }
+}
\ No newline at end of file
diff --git a/app/src/main/res/drawable/ic_height.xml b/app/src/main/res/drawable/ic_height.xml
new file mode 100644
index 0000000..a7bd381
--- /dev/null
+++ b/app/src/main/res/drawable/ic_height.xml
@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:fillColor="#FF000000"
+        android:pathData="M13,6.99h3L12,3L8,6.99h3v10.02H8L12,21l4,-3.99h-3z"/>
+</vector>
\ No newline at end of file
diff --git a/app/src/main/res/drawable/ic_weight.xml b/app/src/main/res/drawable/ic_weight.xml
new file mode 100644
index 0000000..5920585
--- /dev/null
+++ b/app/src/main/res/drawable/ic_weight.xml
@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:fillColor="#FF000000"
+        android:pathData="M12,3C10.34,3 9,4.34 9,6c0,1.1 0.6,2.05 1.48,2.58L7.08,18H4v3h16v-3h-3.08l-3.4,-9.42C14.4,8.05 15,7.1 15,6C15,4.34 13.66,3 12,3zM12,5c0.55,0 1,0.45 1,1s-0.45,1 -1,1 -1,-0.45 -1,-1S11.45,5 12,5z"/>
+</vector>
\ No newline at end of file
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 04e6db2..05341a5 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -1,25 +1,18 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--
-  ~ Copyright (C) 2023 The Android Open Source Project
-  ~
-  ~ Licensed under the Apache License, Version 2.0 (the "License");
-  ~ you may not use this file except in compliance with the License.
-  ~ You may obtain a copy of the License at
-  ~
-  ~      https://www.apache.org/licenses/LICENSE-2.0
-  ~
-  ~ Unless required by applicable law or agreed to in writing, software
-  ~ distributed under the License is distributed on an "AS IS" BASIS,
-  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  ~ See the License for the specific language governing permissions and
-  ~ limitations under the License.
-  -->
 <resources>
     <string name="app_name">BMI Calculator</string>
-    <string name="calculate_tip">Calculate BMI</string>
-    <string name="height">Tinggi Badan</string>
-    <string name="weight">Berat Badan</string>
-    <string name="use_usc">Gunakan Unit USC (lbs/in)?</string>
-    <string name="bmi_calculation">BMI Anda: %s</string>
-    <string name="bmi_category">Kategori: %s</string>
-</resources>
+    <string name="app_title">BMI Calculator</string>
+    <string name="app_subtitle">Calculate your Body Mass Index</string>
+
+    <!-- Input Labels -->
+    <string name="height_cm">Height (cm)</string>
+    <string name="height_inches">Height (inches)</string>
+    <string name="weight_kg">Weight (kg)</string>
+    <string name="weight_lbs">Weight (lbs)</string>
+
+    <!-- Unit System -->
+    <string name="unit_system">Unit System</string>
+
+    <!-- Results -->
+    <string name="your_bmi">Your BMI</string>
+    <string name="bmi_categories_title">BMI Categories</string>
+</resources>
\ No newline at end of file
diff --git a/app/src/test/java/com/example/tiptime/BMICalculatorTest.kt b/app/src/test/java/com/example/tiptime/BMICalculatorTest.kt
new file mode 100644
index 0000000..92abe46
--- /dev/null
+++ b/app/src/test/java/com/example/tiptime/BMICalculatorTest.kt
@@ -0,0 +1,338 @@
+/**
+ * Unit tests untuk BMI Calculator
+ *
+ * NPM: [ISI NPM ANDA]
+ * Nama: [ISI NAMA ANDA]
+ *
+ * Deskripsi: File ini berisi unit test untuk menguji fungsi-fungsi
+ * perhitungan BMI, kategori BMI, dan validasi input.
+ *
+ * Cara menjalankan test:
+ * 1. Di Android Studio, klik kanan pada file ini
+ * 2. Pilih "Run 'BMICalculatorTest'"
+ * Atau jalankan via terminal: ./gradlew test
+ */
+
+package com.example.tiptime
+
+import org.junit.Test
+import org.junit.Assert.*
+
+/**
+ * Unit Test Class untuk BMI Calculator
+ * Menguji semua fungsi kalkulasi dan validasi
+ */
+class BMICalculatorTest {
+
+    /**
+     * Test 1: Menguji perhitungan BMI dengan sistem metrik (cm, kg)
+     * Input: Tinggi 170 cm, Berat 70 kg
+     * Expected Output: BMI = 24.22
+     */
+    @Test
+    fun calculateBMI_metricSystem_returnsCorrectValue() {
+        // Arrange (Persiapan)
+        val height = 170.0
+        val weight = 70.0
+        val useUSC = false
+
+        // Act (Eksekusi)
+        val result = calculateBMI(height, weight, useUSC)
+
+        // Assert (Verifikasi)
+        // BMI = 70 / (1.7 * 1.7) = 24.22
+        assertEquals(24.22, result, 0.01)
+    }
+
+    /**
+     * Test 2: Menguji perhitungan BMI dengan sistem USC (inches, lbs)
+     * Input: Tinggi 67 inches, Berat 154 lbs
+     * Expected Output: BMI ≈ 24.12
+     */
+    @Test
+    fun calculateBMI_uscSystem_returnsCorrectValue() {
+        val height = 67.0
+        val weight = 154.0
+        val useUSC = true
+
+        val result = calculateBMI(height, weight, useUSC)
+
+        // Konversi: 67 in = 1.7018 m, 154 lbs = 69.85 kg
+        // BMI = 69.85 / (1.7018)^2 = 24.12
+        assertEquals(24.12, result, 0.1)
+    }
+
+    /**
+     * Test 3: Menguji edge case - tinggi = 0
+     * Input: Tinggi 0 cm
+     * Expected Output: BMI = 0 (untuk menghindari division by zero)
+     */
+    @Test
+    fun calculateBMI_zeroHeight_returnsZero() {
+        val result = calculateBMI(0.0, 70.0, false)
+        assertEquals(0.0, result, 0.01)
+    }
+
+    /**
+     * Test 4: Menguji edge case - berat = 0
+     * Input: Berat 0 kg
+     * Expected Output: BMI = 0
+     */
+    @Test
+    fun calculateBMI_zeroWeight_returnsZero() {
+        val result = calculateBMI(170.0, 0.0, false)
+        assertEquals(0.0, result, 0.01)
+    }
+
+    /**
+     * Test 5: Menguji kategori BMI - Underweight
+     * Input: BMI = 17.5
+     * Expected Output: "Underweight"
+     */
+    @Test
+    fun calculateBMICategory_underweight_returnsCorrectCategory() {
+        val bmi = 17.5
+        val result = calculateBMICategory(bmi)
+        assertEquals("Underweight", result)
+    }
+
+    /**
+     * Test 6: Menguji kategori BMI - Normal
+     * Input: BMI = 22.0
+     * Expected Output: "Normal"
+     */
+    @Test
+    fun calculateBMICategory_normal_returnsCorrectCategory() {
+        val bmi = 22.0
+        val result = calculateBMICategory(bmi)
+        assertEquals("Normal", result)
+    }
+
+    /**
+     * Test 7: Menguji kategori BMI - Overweight
+     * Input: BMI = 27.5
+     * Expected Output: "Overweight"
+     */
+    @Test
+    fun calculateBMICategory_overweight_returnsCorrectCategory() {
+        val bmi = 27.5
+        val result = calculateBMICategory(bmi)
+        assertEquals("Overweight", result)
+    }
+
+    /**
+     * Test 8: Menguji kategori BMI - Obese
+     * Input: BMI = 32.0
+     * Expected Output: "Obese"
+     */
+    @Test
+    fun calculateBMICategory_obese_returnsCorrectCategory() {
+        val bmi = 32.0
+        val result = calculateBMICategory(bmi)
+        assertEquals("Obese", result)
+    }
+
+    /**
+     * Test 9: Menguji boundary case - BMI = 18.5 (batas Normal)
+     * Input: BMI = 18.5
+     * Expected Output: "Normal"
+     */
+    @Test
+    fun calculateBMICategory_boundaryCase_18point5_returnsNormal() {
+        val bmi = 18.5
+        val result = calculateBMICategory(bmi)
+        assertEquals("Normal", result)
+    }
+
+    /**
+     * Test 10: Menguji boundary case - BMI = 25.0 (batas Overweight)
+     * Input: BMI = 25.0
+     * Expected Output: "Overweight"
+     */
+    @Test
+    fun calculateBMICategory_boundaryCase_25_returnsOverweight() {
+        val bmi = 25.0
+        val result = calculateBMICategory(bmi)
+        assertEquals("Overweight", result)
+    }
+
+    /**
+     * Test 11: Menguji boundary case - BMI = 30.0 (batas Obese)
+     * Input: BMI = 30.0
+     * Expected Output: "Obese"
+     */
+    @Test
+    fun calculateBMICategory_boundaryCase_30_returnsObese() {
+        val bmi = 30.0
+        val result = calculateBMICategory(bmi)
+        assertEquals("Obese", result)
+    }
+
+    /**
+     * Test 12: Menguji validasi input yang valid (metrik)
+     * Input: Tinggi 170 cm, Berat 70 kg
+     * Expected Output: null (tidak ada error)
+     */
+    @Test
+    fun validateInput_validMetricInput_returnsNull() {
+        val result = validateInput(170.0, 70.0, false)
+        assertNull(result)
+    }
+
+    /**
+     * Test 13: Menguji validasi input yang valid (USC)
+     * Input: Tinggi 67 inches, Berat 154 lbs
+     * Expected Output: null (tidak ada error)
+     */
+    @Test
+    fun validateInput_validUSCInput_returnsNull() {
+        val result = validateInput(67.0, 154.0, true)
+        assertNull(result)
+    }
+
+    /**
+     * Test 14: Menguji validasi input - tinggi = 0
+     * Input: Tinggi 0 cm
+     * Expected Output: error message (not null)
+     */
+    @Test
+    fun validateInput_zeroHeight_returnsError() {
+        val result = validateInput(0.0, 70.0, false)
+        assertNotNull(result)
+    }
+
+    /**
+     * Test 15: Menguji validasi input - berat = 0
+     * Input: Berat 0 kg
+     * Expected Output: error message (not null)
+     */
+    @Test
+    fun validateInput_zeroWeight_returnsError() {
+        val result = validateInput(170.0, 0.0, false)
+        assertNotNull(result)
+    }
+
+    /**
+     * Test 16: Menguji validasi input - tinggi terlalu rendah (metrik)
+     * Input: Tinggi 40 cm (tidak realistis)
+     * Expected Output: error message (not null)
+     */
+    @Test
+    fun validateInput_heightTooLowMetric_returnsError() {
+        val result = validateInput(40.0, 70.0, false)
+        assertNotNull(result)
+    }
+
+    /**
+     * Test 17: Menguji validasi input - tinggi terlalu tinggi (metrik)
+     * Input: Tinggi 350 cm (tidak realistis)
+     * Expected Output: error message (not null)
+     */
+    @Test
+    fun validateInput_heightTooHighMetric_returnsError() {
+        val result = validateInput(350.0, 70.0, false)
+        assertNotNull(result)
+    }
+
+    /**
+     * Test 18: Menguji validasi input - berat terlalu rendah (metrik)
+     * Input: Berat 5 kg (tidak realistis)
+     * Expected Output: error message (not null)
+     */
+    @Test
+    fun validateInput_weightTooLowMetric_returnsError() {
+        val result = validateInput(170.0, 5.0, false)
+        assertNotNull(result)
+    }
+
+    /**
+     * Test 19: Menguji validasi input - berat terlalu tinggi (metrik)
+     * Input: Berat 600 kg (tidak realistis)
+     * Expected Output: error message (not null)
+     */
+    @Test
+    fun validateInput_weightTooHighMetric_returnsError() {
+        val result = validateInput(170.0, 600.0, false)
+        assertNotNull(result)
+    }
+
+    /**
+     * Test 20: Menguji perhitungan BMI dengan nilai real world
+     * Input: Tinggi 165 cm, Berat 60 kg
+     * Expected Output: BMI = 22.04
+     */
+    @Test
+    fun calculateBMI_realWorldExample1_returnsCorrectValue() {
+        val height = 165.0
+        val weight = 60.0
+        val useUSC = false
+
+        val result = calculateBMI(height, weight, useUSC)
+
+        // BMI = 60 / (1.65 * 1.65) = 22.04
+        assertEquals(22.04, result, 0.01)
+    }
+
+    /**
+     * Test 21: Menguji perhitungan BMI dengan nilai real world lainnya
+     * Input: Tinggi 180 cm, Berat 85 kg
+     * Expected Output: BMI = 26.23
+     */
+    @Test
+    fun calculateBMI_realWorldExample2_returnsCorrectValue() {
+        val height = 180.0
+        val weight = 85.0
+        val useUSC = false
+
+        val result = calculateBMI(height, weight, useUSC)
+
+        // BMI = 85 / (1.8 * 1.8) = 26.23
+        assertEquals(26.23, result, 0.01)
+    }
+
+    /**
+     * Test 22: Menguji validasi input dengan nilai boundary - tinggi minimum valid
+     * Input: Tinggi 50 cm (batas minimum)
+     * Expected Output: null (valid)
+     */
+    @Test
+    fun validateInput_minimumHeightMetric_returnsNull() {
+        val result = validateInput(50.0, 70.0, false)
+        assertNull(result)
+    }
+
+    /**
+     * Test 23: Menguji validasi input dengan nilai boundary - tinggi maksimum valid
+     * Input: Tinggi 300 cm (batas maksimum)
+     * Expected Output: null (valid)
+     */
+    @Test
+    fun validateInput_maximumHeightMetric_returnsNull() {
+        val result = validateInput(300.0, 70.0, false)
+        assertNull(result)
+    }
+
+    /**
+     * Test 24: Menguji kategori BMI dengan nilai sangat rendah
+     * Input: BMI = 10.0
+     * Expected Output: "Underweight"
+     */
+    @Test
+    fun calculateBMICategory_veryLowBMI_returnsUnderweight() {
+        val bmi = 10.0
+        val result = calculateBMICategory(bmi)
+        assertEquals("Underweight", result)
+    }
+
+    /**
+     * Test 25: Menguji kategori BMI dengan nilai sangat tinggi
+     * Input: BMI = 50.0
+     * Expected Output: "Obese"
+     */
+    @Test
+    fun calculateBMICategory_veryHighBMI_returnsObese() {
+        val bmi = 50.0
+        val result = calculateBMICategory(bmi)
+        assertEquals("Obese", result)
+    }
+}
\ No newline at end of file