diff --git a/.idea/caches/build_file_checksums.ser b/.idea/caches/build_file_checksums.ser
new file mode 100644
index 0000000..a76a424
Binary files /dev/null and b/.idea/caches/build_file_checksums.ser differ
diff --git a/.idea/codeStyles/Project.xml b/.idea/codeStyles/Project.xml
new file mode 100644
index 0000000..30aa626
--- /dev/null
+++ b/.idea/codeStyles/Project.xml
@@ -0,0 +1,29 @@
+<component name="ProjectCodeStyleConfiguration">
+  <code_scheme name="Project" version="173">
+    <Objective-C-extensions>
+      <file>
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Import" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Macro" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Typedef" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Enum" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Constant" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Global" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Struct" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="FunctionPredecl" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Function" />
+      </file>
+      <class>
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Property" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Synthesize" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="InitMethod" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="StaticMethod" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="InstanceMethod" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="DeallocMethod" />
+      </class>
+      <extensions>
+        <pair source="cpp" header="h" fileNamingConvention="NONE" />
+        <pair source="c" header="h" fileNamingConvention="NONE" />
+      </extensions>
+    </Objective-C-extensions>
+  </code_scheme>
+</component>
\ No newline at end of file
diff --git a/.idea/compiler.xml b/.idea/compiler.xml
deleted file mode 100644
index 96cc43e..0000000
--- a/.idea/compiler.xml
+++ /dev/null
@@ -1,22 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="CompilerConfiguration">
-    <resourceExtensions />
-    <wildcardResourcePatterns>
-      <entry name="!?*.java" />
-      <entry name="!?*.form" />
-      <entry name="!?*.class" />
-      <entry name="!?*.groovy" />
-      <entry name="!?*.scala" />
-      <entry name="!?*.flex" />
-      <entry name="!?*.kt" />
-      <entry name="!?*.clj" />
-      <entry name="!?*.aj" />
-    </wildcardResourcePatterns>
-    <annotationProcessing>
-      <profile default="true" name="Default" enabled="false">
-        <processorPath useClasspath="true" />
-      </profile>
-    </annotationProcessing>
-  </component>
-</project>
\ No newline at end of file
diff --git a/.idea/copyright/profiles_settings.xml b/.idea/copyright/profiles_settings.xml
deleted file mode 100644
index e7bedf3..0000000
--- a/.idea/copyright/profiles_settings.xml
+++ /dev/null
@@ -1,3 +0,0 @@
-<component name="CopyrightManager">
-  <settings default="" />
-</component>
\ No newline at end of file
diff --git a/.idea/misc.xml b/.idea/misc.xml
index ba7052b..99202cc 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -5,11 +5,12 @@
     <option name="myDefaultNotNull" value="android.support.annotation.NonNull" />
     <option name="myNullables">
       <value>
-        <list size="4">
+        <list size="5">
           <item index="0" class="java.lang.String" itemvalue="org.jetbrains.annotations.Nullable" />
           <item index="1" class="java.lang.String" itemvalue="javax.annotation.Nullable" />
-          <item index="2" class="java.lang.String" itemvalue="edu.umd.cs.findbugs.annotations.Nullable" />
-          <item index="3" class="java.lang.String" itemvalue="android.support.annotation.Nullable" />
+          <item index="2" class="java.lang.String" itemvalue="javax.annotation.CheckForNull" />
+          <item index="3" class="java.lang.String" itemvalue="edu.umd.cs.findbugs.annotations.Nullable" />
+          <item index="4" class="java.lang.String" itemvalue="android.support.annotation.Nullable" />
         </list>
       </value>
     </option>
@@ -24,7 +25,7 @@
       </value>
     </option>
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_7" default="true" project-jdk-name="1.8" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_7" project-jdk-name="1.8" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/build/classes" />
   </component>
   <component name="ProjectType">
diff --git a/.idea/modules.xml b/.idea/modules.xml
index 6169877..3480a4a 100644
--- a/.idea/modules.xml
+++ b/.idea/modules.xml
@@ -2,7 +2,6 @@
 <project version="4">
   <component name="ProjectModuleManager">
     <modules>
-      <module fileurl="file://$PROJECT_DIR$/CalculaterHacktober.iml" filepath="$PROJECT_DIR$/CalculaterHacktober.iml" />
       <module fileurl="file://$PROJECT_DIR$/CalculatorHacktober.iml" filepath="$PROJECT_DIR$/CalculatorHacktober.iml" />
       <module fileurl="file://$PROJECT_DIR$/app/app.iml" filepath="$PROJECT_DIR$/app/app.iml" />
     </modules>
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
index 94a25f7..35eb1dd 100644
--- a/.idea/vcs.xml
+++ b/.idea/vcs.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="VcsDirectoryMappings">
-    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+    <mapping directory="" vcs="Git" />
   </component>
 </project>
\ No newline at end of file
diff --git a/app/src/main/java/tech/iosd/calculaterhacktober/MainActivity.java b/app/src/main/java/tech/iosd/calculaterhacktober/MainActivity.java
index a0cb52b..44f283b 100644
--- a/app/src/main/java/tech/iosd/calculaterhacktober/MainActivity.java
+++ b/app/src/main/java/tech/iosd/calculaterhacktober/MainActivity.java
@@ -13,6 +13,9 @@ public class MainActivity extends AppCompatActivity {
     Button add,sub,div,mul,one,two,three,four,five,six,seven,eight,nine,zero,equal,clear,decimal,clearall,percent,change,sign;
 
     TextView edit2,edit1;
+    String[] history = new String[5];
+    String formula;
+    int count=0;
     float value1,value2;
     float ans=0;
     boolean addition,subtraction,division,multiplication,answer;
@@ -219,22 +222,40 @@ public void onClick(View view) {
                     answer=true;
                     if(addition==true){
                         ans=value1+value2;
+                        formula=Float.toString(value1)+"+"+Float.toString(value2)+System.getProperty("line.separator")+Float.toString(ans);
                         //addition=false;
                     }
                     else if(subtraction==true){
                         ans=value1-value2;
+                        formula=Float.toString(value1)+"-"+Float.toString(value2)+System.getProperty("line.separator")+Float.toString(ans);
                         //subtraction=false;
                     }
                     else if(division==true){
                         ans=value1/value2;
+                        formula=Float.toString(value1)+"//"+Float.toString(value2)+System.getProperty("line.separator")+Float.toString(ans);
                         //division=false;
                     }
                     else if(multiplication==true){
                         ans=value1*value2;
+                        formula=Float.toString(value1)+"*"+Float.toString(value2)+System.getProperty("line.separator")+Float.toString(ans);
                         //multiplication=false;
 
                     }
                     edit1.setText(ans+"");
+
+                    if(count<=4)
+                    {
+                        history[count]=formula;
+                        count++;
+                    }
+                    else
+                    {
+                        for(int i =0; i<4; i++)
+                        {
+                            history[i]=history[i+1];
+                        }
+                        history[4]=formula;
+                    }
                 }
                 catch (Exception e){
                     edit1.setText("error");
diff --git a/build.gradle b/build.gradle
index c33a638..f93d608 100644
--- a/build.gradle
+++ b/build.gradle
@@ -3,6 +3,7 @@
 buildscript {
     repositories {
         jcenter()
+        google()
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:3.0.0'
@@ -15,6 +16,7 @@ buildscript {
 allprojects {
     repositories {
         jcenter()
+        google()
     }
 }