diff --git a/src/main/c/Stefan/slot_machine.c b/src/main/c/Stefan/slot_machine.c
index 4d1e33f..ef586f5 100644
--- a/src/main/c/Stefan/slot_machine.c
+++ b/src/main/c/Stefan/slot_machine.c
@@ -10,8 +10,7 @@ void slotMachine(){
     while(balance > 0){
 
         int bet = getBet(balance);
-        balance -= bet;
-        printf("%d\n", balance);
+        balance = subtractBetFromBalance(bet, balance);
     }
 
 
@@ -47,6 +46,10 @@ int getBet(int balance){
     }
 }
 
+int subtractBetFromBalance(int bet, int balance){
+    return balance - bet;
+}
+
 void welcomeMessage(){
     printf("Herzlich Willkommen zur \n\n"
            "     _       _                           _     _            \n"
diff --git a/src/main/c/Stefan/slot_machine.h b/src/main/c/Stefan/slot_machine.h
index 14a3217..b0119f4 100644
--- a/src/main/c/Stefan/slot_machine.h
+++ b/src/main/c/Stefan/slot_machine.h
@@ -6,5 +6,6 @@ void welcomeMessage();
 int getBalance();
 int userInput();
 int getBet(int balance);
+int subtractBetFromBalance(int bet, int balance);
 
 #endif // SLOT_MACHINE_H
\ No newline at end of file
diff --git a/src/test/c/Stefan/test_slot_machine.c b/src/test/c/Stefan/test_slot_machine.c
index b327568..4afa387 100644
--- a/src/test/c/Stefan/test_slot_machine.c
+++ b/src/test/c/Stefan/test_slot_machine.c
@@ -5,4 +5,14 @@ void setUp() {}
 
 void tearDown() {}
 
-void test_test(){}
\ No newline at end of file
+void test_subtract_bet_10_from_balance_10() {
+
+    //arrange
+    int expectedResult = 0;
+
+    //act
+    int actualResult = subtractBetFromBalance(10, 10);
+
+    //assert
+    TEST_ASSERT_EQUAL_INT(expectedResult, actualResult);
+}
\ No newline at end of file