diff --git a/src/main/c/taschenrechner.h b/src/main/c/taschenrechner.h
index 6b7955b..aedb4f3 100644
--- a/src/main/c/taschenrechner.h
+++ b/src/main/c/taschenrechner.h
@@ -1,22 +1,22 @@
 #ifndef TASCHENRECHNER_H
 #define TASCHENRECHNER_H
 
-//add function
+// add function
 double add(double a, double b);
 
-//minus function
+// minus function
 double minus(double a, double b);
 
-//multiply function
+// multiply function
 double multiply(double a, double b);
 
-//divide function
+// divide function
 double divide(double a, double b);
 
-//get input and check if its a number
+// get input and check if its a number
 double testForNumber();
 
-//get input and check if its a operator
+// get input and check if its a operator
 char testForOperator();
 
 // Square root function
@@ -56,7 +56,7 @@ int mode(int userChoice);
 
 int displayMenu();
 
-//Conversion Functions
+// Conversion Functions
 double ConMeter(double meter, int startingUnit, int endingUnit);
 
 double ConMeterToFoot(double distance, int startingUnit, int endingUnit);
diff --git a/src/test/c/test_taschenrechner.c b/src/test/c/test_taschenrechner.c
index f51aaad..33f7f6c 100644
--- a/src/test/c/test_taschenrechner.c
+++ b/src/test/c/test_taschenrechner.c
@@ -156,4 +156,40 @@ void test_exponentialFunction(void) {
     TEST_ASSERT_EQUAL_FLOAT(1.0, exponentialFunction(0.0));
 }
 
+// Test case for subtraction
+void test_performOperation_Subtraction(void) {
+    // Arrange
+    int result;
+
+    // Act
+    result = performOperation(10, '-', 3);
+
+    // Assert
+    TEST_ASSERT_EQUAL_INT(7, result);
+}
+
+// Test case for multiplication
+void test_performOperation_Multiplication(void) {
+    // Arrange
+    int result;
+
+    // Act
+    result = performOperation(4, '*', 6);
+
+    // Assert
+    TEST_ASSERT_EQUAL_INT(24, result);
+}
+
+// Test case for division
+void test_performOperation_Division(void) {
+    // Arrange
+    int result;
+
+    // Act
+    result = performOperation(8, '/', 2);
+
+    // Assert
+    TEST_ASSERT_EQUAL_INT(4, result);
+}
+
 #endif // TEST