diff --git a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
index 84c04f21..b110c48b 100644
--- a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -60,6 +60,9 @@ public void pressClearKey() {
      * @param operation "+" für Addition, "-" für Substraktion, "x" für Multiplikation, "/" für Division
      */
     public void pressBinaryOperationKey(String operation)  {
+        if (!latestOperation.isEmpty()) {
+            pressEqualsKey();
+        }
         latestValue = Double.parseDouble(screen);
         latestOperation = operation;
     }
@@ -94,9 +97,12 @@ public void pressUnaryOperationKey(String operation) {
      * Beim zweimaligem Drücken, oder wenn bereits ein Trennzeichen angezeigt wird, passiert nichts.
      */
     public void pressDotKey() {
-        if(!screen.contains(".")) screen = screen + ".";
+        if (!screen.contains(".")) {
+            screen = screen + ".";
+        }
     }
 
+
     /**
      * Empfängt den Befehl der gedrückten Vorzeichenumkehrstaste ("+/-").
      * Zeigt der Bildschirm einen positiven Wert an, so wird ein "-" links angehängt, der Bildschirm
@@ -118,6 +124,9 @@ public void pressNegativeKey() {
      * und das Ergebnis direkt angezeigt.
      */
     public void pressEqualsKey() {
+        if(latestOperation.isEmpty()) {
+            return;
+        }
         var result = switch(latestOperation) {
             case "+" -> latestValue + Double.parseDouble(screen);
             case "-" -> latestValue - Double.parseDouble(screen);
diff --git a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
index ddff0daf..c8bd70fa 100644
--- a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -88,7 +88,54 @@ void testMultipleDecimalDots() {
         assertEquals(expected, actual);
     }
 
+//Teilaufgabe 1:
+    @Test
+    @DisplayName("should display result after subtracting two positive multi-digit numbers")
+    void testNegativeAddition() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(7);
+        calc.pressDigitKey(1);
+        calc.pressBinaryOperationKey("-");
+        calc.pressDigitKey(5);
+        calc.pressDigitKey(1);
+        calc.pressEqualsKey();
+
+        String expected = "20";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+//Teilaufgabe 2 - Test 1:
+    @Test
+    @DisplayName("tests if the calculator uses the latest result to continue calculating")
+    void testMultipleAddition() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(7);
+        calc.pressBinaryOperationKey("+");
+        calc.pressDigitKey(5);
+        calc.pressBinaryOperationKey("+");
+        calc.pressDigitKey(1);
+        calc.pressEqualsKey();
+
+        String expected = "13";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+//Teilaufgabe 2 - Test 2:
+    @Test
+    @DisplayName("tests if 0 is displayed after pressing the equal key when not pressed a digit before")
+    void testEqualsKey() {
+        Calculator calc = new Calculator();
+        calc.pressEqualsKey();
+        String expected = "0";
+        String actual = calc.readScreen();
 
-    //TODO hier weitere Tests erstellen
+        assertEquals(expected, actual);
 }
 
+
+
+}
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