diff --git a/app/build.gradle b/app/build.gradle
index 87c968c..bd11c60 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -23,4 +23,5 @@ dependencies {
     compile fileTree(dir: 'libs', include: ['*.jar'])
     testCompile 'junit:junit:4.12'
     compile 'com.android.support:appcompat-v7:23.1.1'
+    compile 'com.jakewharton:butterknife:7.0.1'
 }
diff --git a/app/proguard-rules.pro b/app/proguard-rules.pro
index bbaa5f0..aaf6b8c 100644
--- a/app/proguard-rules.pro
+++ b/app/proguard-rules.pro
@@ -1,6 +1,6 @@
 # Add project specific ProGuard rules here.
 # By default, the flags in this file are appended to flags specified
-# in /home/tibbi/misc/sdk/tools/proguard/proguard-android.txt
+# in $ANDROID_HOME/tools/proguard/proguard-android.txt
 # You can edit the include path and order by changing the proguardFiles
 # directive in build.gradle.
 #
@@ -15,3 +15,15 @@
 #-keepclassmembers class fqcn.of.javascript.interface.for.webview {
 #   public *;
 #}
+
+-keep class butterknife.** { *; }
+-dontwarn butterknife.internal.**
+-keep class **$$ViewBinder { *; }
+
+-keepclasseswithmembernames class * {
+    @butterknife.* <fields>;
+}
+
+-keepclasseswithmembernames class * {
+    @butterknife.* <methods>;
+}
diff --git a/app/src/main/java/calculator/simplemobiletools/com/simple_calculator/MainActivity.java b/app/src/main/java/calculator/simplemobiletools/com/simple_calculator/MainActivity.java
index 7025cee..d6a63c4 100644
--- a/app/src/main/java/calculator/simplemobiletools/com/simple_calculator/MainActivity.java
+++ b/app/src/main/java/calculator/simplemobiletools/com/simple_calculator/MainActivity.java
@@ -1,13 +1,77 @@
 package calculator.simplemobiletools.com.simple_calculator;
 
-import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
+import android.support.v7.app.AppCompatActivity;
+import android.view.View;
+import android.widget.TextView;
+
+import butterknife.Bind;
+import butterknife.ButterKnife;
+import butterknife.OnClick;
 
 public class MainActivity extends AppCompatActivity {
+    @Bind(R.id.result) TextView result;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
+        ButterKnife.bind(this);
+    }
+
+    private void addDigit(int number) {
+        final String currentValue = result.getText().toString();
+        final String newValue = getFormattedValue(currentValue + number);
+        result.setText(newValue);
+    }
+
+    private String getFormattedValue(String str) {
+        return formatDouble(Double.parseDouble(str));
+    }
+
+    private String formatDouble(double d) {
+        if (d == (long) d) {
+            return String.format("%d", (long) d);
+        } else {
+            return String.format("%s", d);
+        }
+    }
+
+    @OnClick({R.id.btn_0, R.id.btn_1, R.id.btn_2, R.id.btn_3, R.id.btn_4, R.id.btn_5, R.id.btn_6, R.id.btn_7, R.id.btn_8, R.id.btn_9})
+    public void digitClicked(View view) {
+        switch (view.getId()) {
+            case R.id.btn_0:
+                addDigit(0);
+                break;
+            case R.id.btn_1:
+                addDigit(1);
+                break;
+            case R.id.btn_2:
+                addDigit(2);
+                break;
+            case R.id.btn_3:
+                addDigit(3);
+                break;
+            case R.id.btn_4:
+                addDigit(4);
+                break;
+            case R.id.btn_5:
+                addDigit(5);
+                break;
+            case R.id.btn_6:
+                addDigit(6);
+                break;
+            case R.id.btn_7:
+                addDigit(7);
+                break;
+            case R.id.btn_8:
+                addDigit(8);
+                break;
+            case R.id.btn_9:
+                addDigit(9);
+                break;
+            default:
+                break;
+        }
     }
 }
diff --git a/app/src/main/res/layout/activity_main.xml b/app/src/main/res/layout/activity_main.xml
index 0436c6e..1d33929 100644
--- a/app/src/main/res/layout/activity_main.xml
+++ b/app/src/main/res/layout/activity_main.xml
@@ -11,11 +11,13 @@
     tools:context="calculator.simplemobiletools.com.simple_calculator.MainActivity">
 
     <TextView
-        android:id="@+id/display"
+        android:id="@+id/result"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_marginBottom="@dimen/activity_margin"
         android:gravity="right"
+        android:lines="1"
+        android:maxLength="15"
         android:padding="@dimen/activity_margin"
         android:text="0"
         android:textSize="@dimen/display_text_size"/>
@@ -23,7 +25,7 @@
     <TableLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
-        android:layout_below="@+id/display">
+        android:layout_below="@+id/result">
 
         <TableRow
             android:layout_width="match_parent"