diff --git a/.gitignore b/.gitignore
index 496ee2c..2608ec2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
-.DS_Store
\ No newline at end of file
+.DS_Store
+.vscode
\ No newline at end of file
diff --git a/build-project.sh b/build-project.sh
index c75f560..4247c59 100644
--- a/build-project.sh
+++ b/build-project.sh
@@ -1,5 +1,6 @@
 clear
+ceedling test:all
 cd src/
-gcc main.c
+gcc main.c mainMenu.c
 ./a.out
-rm a.out
\ No newline at end of file
+rm a.out
diff --git a/build/test/cache/defines_dependency.yml b/build/test/cache/defines_dependency.yml
new file mode 100644
index 0000000..217b8d2
--- /dev/null
+++ b/build/test/cache/defines_dependency.yml
@@ -0,0 +1,3 @@
+---
+src/updateCustomerAccountBalance.c:
+- TEST
diff --git a/build/test/cache/input.yml b/build/test/cache/input.yml
new file mode 100644
index 0000000..bc8023f
--- /dev/null
+++ b/build/test/cache/input.yml
@@ -0,0 +1,242 @@
+---
+:project:
+  :use_exceptions: false
+  :use_mocks: true
+  :compile_threads: 1
+  :test_threads: 1
+  :use_test_preprocessor: true
+  :use_preprocessor_directives: false
+  :use_deep_dependencies: false
+  :generate_deep_dependencies: true
+  :auto_link_deep_dependencies: false
+  :test_file_prefix: test_
+  :options_paths: []
+  :release_build: false
+  :use_auxiliary_dependencies: true
+  :build_root: build
+  :which_ceedling: gem
+  :ceedling_version: 0.31.1
+  :default_tasks:
+  - test:all
+:release_build:
+  :use_assembly: false
+  :artifacts: []
+:paths:
+  :test:
+  - "+:tests/**"
+  - "-:tests/support"
+  :source:
+  - src/**
+  :support:
+  - tests/support
+  :include: []
+  :libraries: []
+  :test_toolchain_include: []
+  :release_toolchain_include: []
+:files:
+  :test: []
+  :source: []
+  :assembly: []
+  :support: []
+  :include: []
+:environment:
+- :rake_columns: '120'
+:defines:
+  :test:
+  - &1 []
+  - TEST
+  :test_preprocess:
+  - *1
+  - TEST
+  :release: []
+  :release_preprocess: []
+  :use_test_definition: false
+  :common: []
+:libraries:
+  :flag: "-l${1}"
+  :path_flag: "-L ${1}"
+  :test: []
+  :test_preprocess: []
+  :release: []
+  :release_preprocess: []
+  :placement: :end
+  :system: []
+:flags: {}
+:extension:
+  :header: ".h"
+  :source: ".c"
+  :assembly: ".s"
+  :object: ".o"
+  :libraries:
+  - ".a"
+  - ".so"
+  :executable: ".out"
+  :map: ".map"
+  :list: ".lst"
+  :testpass: ".pass"
+  :testfail: ".fail"
+  :dependencies: ".d"
+:unity:
+  :vendor_path: "/Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor"
+  :defines: []
+:cmock:
+  :vendor_path: "/Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor"
+  :defines: []
+  :includes: []
+  :mock_prefix: mock_
+  :when_no_prototypes: :warn
+  :enforce_strict_ordering: true
+  :plugins:
+  - :ignore
+  - :callback
+  :treat_as:
+    uint8: HEX8
+    uint16: HEX16
+    uint32: UINT32
+    int8: INT8
+    bool: UINT8
+  :mock_path: build/test/mocks
+  :verbosity: 3
+  :unity_helper: false
+:cexception:
+  :vendor_path: "/Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor"
+  :defines: []
+:test_runner:
+  :includes: []
+  :file_suffix: _runner
+:tools:
+  :test_compiler:
+    :executable: gcc
+    :name: default_test_compiler
+    :stderr_redirect: :none
+    :background_exec: :none
+    :optional: false
+    :arguments:
+    - ''
+    - ''
+    - -I"$": COLLECTION_PATHS_TEST_SUPPORT_SOURCE_INCLUDE_VENDOR
+    - -I"$": COLLECTION_PATHS_TEST_TOOLCHAIN_INCLUDE
+    - "-D$": COLLECTION_DEFINES_TEST_AND_VENDOR
+    - "-DGNU_COMPILER"
+    - "-g"
+    - ''
+    - -c "${1}"
+    - -o "${2}"
+    - "-MMD"
+    - -MF "${4}"
+  :test_fixture:
+    :executable: "${1}"
+    :name: default_test_fixture
+    :stderr_redirect: :auto
+    :background_exec: :none
+    :optional: false
+    :arguments: []
+  :test_linker:
+    :executable: gcc
+    :name: default_test_linker
+    :stderr_redirect: :none
+    :background_exec: :none
+    :optional: false
+    :arguments:
+    - ''
+    - ''
+    - ''
+    - '"${1}"'
+    - "${5}"
+    - -o "${2}"
+    - ''
+    - "${4}"
+    - ''
+  :test_file_preprocessor:
+    :executable: gcc
+    :name: default_test_file_preprocessor
+    :stderr_redirect: :none
+    :background_exec: :none
+    :optional: false
+    :arguments:
+    - ''
+    - ''
+    - "-E"
+    - -I"$": COLLECTION_PATHS_TEST_SUPPORT_SOURCE_INCLUDE_VENDOR
+    - -I"$": COLLECTION_PATHS_TEST_TOOLCHAIN_INCLUDE
+    - "-D$": COLLECTION_DEFINES_TEST_AND_VENDOR
+    - "-D$": DEFINES_TEST_PREPROCESS
+    - "-DGNU_COMPILER"
+    - '"${1}"'
+    - -o "${2}"
+  :test_file_preprocessor_directives:
+    :executable: gcc
+    :name: default_test_file_preprocessor_directives
+    :stderr_redirect: :none
+    :background_exec: :none
+    :optional: false
+    :arguments:
+    - "-E"
+    - -I"$": COLLECTION_PATHS_TEST_SUPPORT_SOURCE_INCLUDE_VENDOR
+    - -I"$": COLLECTION_PATHS_TEST_TOOLCHAIN_INCLUDE
+    - "-D$": COLLECTION_DEFINES_TEST_AND_VENDOR
+    - "-D$": DEFINES_TEST_PREPROCESS
+    - "-DGNU_COMPILER"
+    - "-fdirectives-only"
+    - '"${1}"'
+    - -o "${2}"
+  :test_includes_preprocessor:
+    :executable: gcc
+    :name: default_test_includes_preprocessor
+    :stderr_redirect: :none
+    :background_exec: :none
+    :optional: false
+    :arguments:
+    - ''
+    - ''
+    - "-E"
+    - "-MM"
+    - "-MG"
+    - -I"$": COLLECTION_PATHS_TEST_SUPPORT_SOURCE_INCLUDE_VENDOR
+    - -I"$": COLLECTION_PATHS_TEST_TOOLCHAIN_INCLUDE
+    - "-D$": COLLECTION_DEFINES_TEST_AND_VENDOR
+    - "-D$": DEFINES_TEST_PREPROCESS
+    - "-DGNU_COMPILER"
+    - '"${1}"'
+:test_compiler:
+  :arguments: []
+:test_linker:
+  :arguments: []
+:test_fixture:
+  :arguments: []
+  :link_objects: []
+:test_includes_preprocessor:
+  :arguments: []
+:test_file_preprocessor:
+  :arguments: []
+:test_file_preprocessor_directives:
+  :arguments: []
+:test_dependencies_generator:
+  :arguments: []
+:release_compiler:
+  :arguments: []
+:release_linker:
+  :arguments: []
+:release_assembler:
+  :arguments: []
+:release_dependencies_generator:
+  :arguments: []
+:plugins:
+  :load_paths:
+  - "/Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/lib/../plugins"
+  :enabled:
+  - stdout_pretty_tests_report
+  - module_generator
+  :display_raw_test_results: false
+  :stdout_pretty_tests_report_path: "/Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/lib/../plugins/stdout_pretty_tests_report"
+  :module_generator_path: "/Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/lib/../plugins/module_generator"
+:gcov:
+  :reports:
+  - HtmlDetailed
+  :gcovr:
+    :html_medium_threshold: 75
+    :html_high_threshold: 90
+:module_generator:
+  :project_root: "./"
+  :source_root: src/
+  :test_root: test/
diff --git a/build/test/cache/test_updateCustomerAccountBalance.c b/build/test/cache/test_updateCustomerAccountBalance.c
new file mode 100644
index 0000000..5b6d44a
--- /dev/null
+++ b/build/test/cache/test_updateCustomerAccountBalance.c
@@ -0,0 +1,63 @@
+#include "src/updateCustomerAccountBalance.h"
+#include "/Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity.h"
+
+
+
+
+
+
+
+
+void setUp(void)
+
+{
+
+}
+
+
+
+void tearDown(void)
+
+{
+
+}
+
+
+
+void test_updateAvailableAccountBalanceSuccess(void){
+
+
+
+ int id1 = 1234;
+
+ int id2 = 1327;
+
+ int id3 = 1666;
+
+
+
+ int newBalance1=500;
+
+ int newBalance2=800;
+
+ int newBalance3=700;
+
+
+
+ _Bool results1=updateAvailableAccountBalance(id1,newBalance1);
+
+ _Bool results2=updateAvailableAccountBalance(id2,newBalance2);
+
+ _Bool results3=updateAvailableAccountBalance(id3,newBalance3);
+
+
+
+ do {if ((results1)) {} else {UnityFail( ((" Expected TRUE Was FALSE")), (UNITY_UINT)((UNITY_UINT)(29)));}} while(0);
+
+ do {if ((results2)) {} else {UnityFail( ((" Expected TRUE Was FALSE")), (UNITY_UINT)((UNITY_UINT)(30)));}} while(0);
+
+ do {if ((results3)) {} else {UnityFail( ((" Expected TRUE Was FALSE")), (UNITY_UINT)((UNITY_UINT)(31)));}} while(0);
+
+
+
+}
diff --git a/build/test/dependencies/cmock.d b/build/test/dependencies/cmock.d
new file mode 100644
index 0000000..58d1e9e
--- /dev/null
+++ b/build/test/dependencies/cmock.d
@@ -0,0 +1,6 @@
+build/test/out/c/cmock.o: \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/cmock/src/cmock.c \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/cmock/src/cmock.h \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/cmock/src/cmock_internals.h \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity.h \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity_internals.h
diff --git a/build/test/dependencies/test_updateCustomerAccountBalance.d b/build/test/dependencies/test_updateCustomerAccountBalance.d
new file mode 100644
index 0000000..506a323
--- /dev/null
+++ b/build/test/dependencies/test_updateCustomerAccountBalance.d
@@ -0,0 +1,5 @@
+build/test/out/c/test_updateCustomerAccountBalance.o: \
+  tests/test_updateCustomerAccountBalance.c \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity.h \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity_internals.h \
+  src/updateCustomerAccountBalance.h
diff --git a/build/test/dependencies/test_updateCustomerAccountBalance_runner.d b/build/test/dependencies/test_updateCustomerAccountBalance_runner.d
new file mode 100644
index 0000000..e38698a
--- /dev/null
+++ b/build/test/dependencies/test_updateCustomerAccountBalance_runner.d
@@ -0,0 +1,4 @@
+build/test/out/c/test_updateCustomerAccountBalance_runner.o: \
+  build/test/runners/test_updateCustomerAccountBalance_runner.c \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity.h \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity_internals.h
diff --git a/build/test/dependencies/unity.d b/build/test/dependencies/unity.d
new file mode 100644
index 0000000..931f713
--- /dev/null
+++ b/build/test/dependencies/unity.d
@@ -0,0 +1,4 @@
+build/test/out/c/unity.o: \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity.c \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity.h \
+  /Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity_internals.h
diff --git a/build/test/dependencies/updateCustomerAccountBalance.d b/build/test/dependencies/updateCustomerAccountBalance.d
new file mode 100644
index 0000000..5f06f3b
--- /dev/null
+++ b/build/test/dependencies/updateCustomerAccountBalance.d
@@ -0,0 +1,5 @@
+build/test/out/c/updateCustomerAccountBalance.o: \
+  src/updateCustomerAccountBalance.c src/updateCustomerAccountBalance.h \
+  src/currentCustomerAccountBalance.c \
+  src/currentCustomerAccountBalance.h src/_file_information.h \
+  src/lineReplacer.h
diff --git a/build/test/out/c/cmock.o b/build/test/out/c/cmock.o
new file mode 100644
index 0000000..7a4b511
Binary files /dev/null and b/build/test/out/c/cmock.o differ
diff --git a/build/test/out/c/test_updateCustomerAccountBalance.o b/build/test/out/c/test_updateCustomerAccountBalance.o
new file mode 100644
index 0000000..fda3468
Binary files /dev/null and b/build/test/out/c/test_updateCustomerAccountBalance.o differ
diff --git a/build/test/out/c/test_updateCustomerAccountBalance_runner.o b/build/test/out/c/test_updateCustomerAccountBalance_runner.o
new file mode 100644
index 0000000..35fab4e
Binary files /dev/null and b/build/test/out/c/test_updateCustomerAccountBalance_runner.o differ
diff --git a/build/test/out/c/unity.o b/build/test/out/c/unity.o
new file mode 100644
index 0000000..cf2d7fe
Binary files /dev/null and b/build/test/out/c/unity.o differ
diff --git a/build/test/out/c/updateCustomerAccountBalance.o b/build/test/out/c/updateCustomerAccountBalance.o
new file mode 100644
index 0000000..3e002d0
Binary files /dev/null and b/build/test/out/c/updateCustomerAccountBalance.o differ
diff --git a/build/test/out/test_updateCustomerAccountBalance.out b/build/test/out/test_updateCustomerAccountBalance.out
new file mode 100755
index 0000000..42268fb
Binary files /dev/null and b/build/test/out/test_updateCustomerAccountBalance.out differ
diff --git a/build/test/preprocess/files/test_updateCustomerAccountBalance.c b/build/test/preprocess/files/test_updateCustomerAccountBalance.c
new file mode 100644
index 0000000..5b6d44a
--- /dev/null
+++ b/build/test/preprocess/files/test_updateCustomerAccountBalance.c
@@ -0,0 +1,63 @@
+#include "src/updateCustomerAccountBalance.h"
+#include "/Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity.h"
+
+
+
+
+
+
+
+
+void setUp(void)
+
+{
+
+}
+
+
+
+void tearDown(void)
+
+{
+
+}
+
+
+
+void test_updateAvailableAccountBalanceSuccess(void){
+
+
+
+ int id1 = 1234;
+
+ int id2 = 1327;
+
+ int id3 = 1666;
+
+
+
+ int newBalance1=500;
+
+ int newBalance2=800;
+
+ int newBalance3=700;
+
+
+
+ _Bool results1=updateAvailableAccountBalance(id1,newBalance1);
+
+ _Bool results2=updateAvailableAccountBalance(id2,newBalance2);
+
+ _Bool results3=updateAvailableAccountBalance(id3,newBalance3);
+
+
+
+ do {if ((results1)) {} else {UnityFail( ((" Expected TRUE Was FALSE")), (UNITY_UINT)((UNITY_UINT)(29)));}} while(0);
+
+ do {if ((results2)) {} else {UnityFail( ((" Expected TRUE Was FALSE")), (UNITY_UINT)((UNITY_UINT)(30)));}} while(0);
+
+ do {if ((results3)) {} else {UnityFail( ((" Expected TRUE Was FALSE")), (UNITY_UINT)((UNITY_UINT)(31)));}} while(0);
+
+
+
+}
diff --git a/build/test/preprocess/includes/test_updateCustomerAccountBalance.c b/build/test/preprocess/includes/test_updateCustomerAccountBalance.c
new file mode 100644
index 0000000..2b0ad02
--- /dev/null
+++ b/build/test/preprocess/includes/test_updateCustomerAccountBalance.c
@@ -0,0 +1,3 @@
+---
+- "/Users/canhacioglu/.rbenv/versions/2.7.7/lib/ruby/gems/2.7.0/gems/ceedling-0.31.1/vendor/unity/src/unity.h"
+- src/updateCustomerAccountBalance.h
diff --git a/build/test/runners/test_updateCustomerAccountBalance_runner.c b/build/test/runners/test_updateCustomerAccountBalance_runner.c
new file mode 100644
index 0000000..887be8b
--- /dev/null
+++ b/build/test/runners/test_updateCustomerAccountBalance_runner.c
@@ -0,0 +1,81 @@
+/* AUTOGENERATED FILE. DO NOT EDIT. */
+
+/*=======Automagically Detected Files To Include=====*/
+#include "unity.h"
+
+int GlobalExpectCount;
+int GlobalVerifyOrder;
+char* GlobalOrderError;
+
+/*=======External Functions This Runner Calls=====*/
+extern void setUp(void);
+extern void tearDown(void);
+extern void test_updateAvailableAccountBalanceSuccess(void);
+
+
+/*=======Mock Management=====*/
+static void CMock_Init(void)
+{
+  GlobalExpectCount = 0;
+  GlobalVerifyOrder = 0;
+  GlobalOrderError = NULL;
+}
+static void CMock_Verify(void)
+{
+}
+static void CMock_Destroy(void)
+{
+}
+
+/*=======Test Reset Options=====*/
+void resetTest(void);
+void resetTest(void)
+{
+  tearDown();
+  CMock_Verify();
+  CMock_Destroy();
+  CMock_Init();
+  setUp();
+}
+void verifyTest(void);
+void verifyTest(void)
+{
+  CMock_Verify();
+}
+
+/*=======Test Runner Used To Run Each Test=====*/
+static void run_test(UnityTestFunction func, const char* name, UNITY_LINE_TYPE line_num)
+{
+    Unity.CurrentTestName = name;
+    Unity.CurrentTestLineNumber = line_num;
+#ifdef UNITY_USE_COMMAND_LINE_ARGS
+    if (!UnityTestMatches())
+        return;
+#endif
+    Unity.NumberOfTests++;
+    UNITY_CLR_DETAILS();
+    UNITY_EXEC_TIME_START();
+    CMock_Init();
+    if (TEST_PROTECT())
+    {
+        setUp();
+        func();
+    }
+    if (TEST_PROTECT())
+    {
+        tearDown();
+        CMock_Verify();
+    }
+    CMock_Destroy();
+    UNITY_EXEC_TIME_STOP();
+    UnityConcludeTest();
+}
+
+/*=======MAIN=====*/
+int main(void)
+{
+  UnityBegin("test_updateCustomerAccountBalance.c");
+  run_test(test_updateAvailableAccountBalanceSuccess, "test_updateAvailableAccountBalanceSuccess", 15);
+
+  return UnityEnd();
+}
diff --git a/project.yml b/project.yml
new file mode 100644
index 0000000..640cb8f
--- /dev/null
+++ b/project.yml
@@ -0,0 +1,101 @@
+---
+
+# Notes:
+# Sample project C code is not presently written to produce a release artifact.
+# As such, release build options are disabled.
+# This sample, therefore, only demonstrates running a collection of unit tests.
+
+:project:
+  :use_exceptions: FALSE
+  :use_test_preprocessor: TRUE
+  :use_auxiliary_dependencies: TRUE
+  :build_root: build
+#  :release_build: TRUE
+  :test_file_prefix: test_
+  :which_ceedling: gem
+  :ceedling_version: 0.31.1
+  :default_tasks:
+    - test:all
+
+#:test_build:
+#  :use_assembly: TRUE
+
+#:release_build:
+#  :output: MyApp.out
+#  :use_assembly: FALSE
+
+:environment:
+
+:extension:
+  :executable: .out
+
+:paths:
+  :test:
+    - +:tests/**
+    - -:tests/support
+  :source:
+    - src/**
+  :support:
+    - tests/support
+  :libraries: []
+
+:defines:
+  # in order to add common defines:
+  #  1) remove the trailing [] from the :common: section
+  #  2) add entries to the :common: section (e.g. :test: has TEST defined)
+  :common: &common_defines []
+  :test:
+    - *common_defines
+    - TEST
+  :test_preprocess:
+    - *common_defines
+    - TEST
+
+:cmock:
+  :mock_prefix: mock_
+  :when_no_prototypes: :warn
+  :enforce_strict_ordering: TRUE
+  :plugins:
+    - :ignore
+    - :callback
+  :treat_as:
+    uint8:    HEX8
+    uint16:   HEX16
+    uint32:   UINT32
+    int8:     INT8
+    bool:     UINT8
+
+# Add -gcov to the plugins list to make sure of the gcov plugin
+# You will need to have gcov and gcovr both installed to make it work.
+# For more information on these options, see docs in plugins/gcov
+:gcov:
+  :reports:
+    - HtmlDetailed
+  :gcovr:
+    :html_medium_threshold: 75
+    :html_high_threshold: 90
+
+#:tools:
+# Ceedling defaults to using gcc for compiling, linking, etc.
+# As [:tools] is blank, gcc will be used (so long as it's in your system path)
+# See documentation to configure a given toolchain for use
+
+# LIBRARIES
+# These libraries are automatically injected into the build process. Those specified as
+# common will be used in all types of builds. Otherwise, libraries can be injected in just
+# tests or releases. These options are MERGED with the options in supplemental yaml files.
+:libraries:
+  :placement: :end
+  :flag: "-l${1}"
+  :path_flag: "-L ${1}"
+  :system: []    # for example, you might list 'm' to grab the math library
+  :test: []
+  :release: []
+
+:plugins:
+  :load_paths:
+    - "#{Ceedling.load_path}"
+  :enabled:
+    - stdout_pretty_tests_report
+    - module_generator
+...
diff --git a/src/CustomerData.txt b/src/CustomerData.txt
new file mode 100644
index 0000000..911b18e
--- /dev/null
+++ b/src/CustomerData.txt
@@ -0,0 +1,20 @@
+1234=example
+ID=1234
+forename=Max
+Surname=Mustermann
+password=example
+balance=5000
+
+1327=example
+ID=1327
+forename=Max
+Surname=Mustermann
+password=example
+balance=1500
+
+1666=example
+ID=1666
+forename=Max
+Surname=Mustermann
+password=example
+balance=240
\ No newline at end of file
diff --git a/src/CustomerProperties.h b/src/CustomerProperties.h
new file mode 100644
index 0000000..2bbab62
--- /dev/null
+++ b/src/CustomerProperties.h
@@ -0,0 +1,4 @@
+typedef struct Customer{
+	char *ID, *forename, *surname, *password;
+	float balance;
+}customer_t;
diff --git a/src/LoginCustomer.c b/src/LoginCustomer.c
new file mode 100644
index 0000000..5c2a7a4
--- /dev/null
+++ b/src/LoginCustomer.c
@@ -0,0 +1,97 @@
+#include "LoginCustomer.h"
+
+bool checkLogin(bool loginSuccessful)
+{	
+	return (loginSuccessful) ? true : false;
+}
+
+void collectCustomerDataForLogin(int attempts)
+{
+	customer_t c;
+	c.ID = calloc(15+1,sizeof(char));
+	c.password = calloc(15+1, sizeof(char));
+	char digitCharacterFromUser, passwordCharacterFromUser;
+	int IDLengthCounter = 0, passwordLengthCounter = 0;
+	const int IDMaxLength = 16, passwordMaxLength = 16;
+	
+	printf("Enter ID:\n");
+	while(((digitCharacterFromUser=getchar()) != '\n')&&IDLengthCounter<IDMaxLength){
+			if(digitCharacterFromUser>='0'&&digitCharacterFromUser<='9'){
+				*(c.ID+IDLengthCounter) = digitCharacterFromUser;
+			}
+			else{
+				printf("Character entered is not a digit. Aborting.\n");
+				exit(-1);
+			}
+		++IDLengthCounter;	
+	}
+	*(c.ID+IDLengthCounter) = '\0';
+	
+	if(IDLengthCounter>=IDMaxLength){
+		printf("ID entered is too long. Aborting.\n");
+		exit(-1);
+	}
+
+	printf("Enter password:\n");
+	while((passwordCharacterFromUser=getchar())!='\n'&&passwordLengthCounter<passwordMaxLength){
+		*(c.password+passwordLengthCounter) = passwordCharacterFromUser;
+		++passwordLengthCounter;
+	}
+	*(c.password+passwordLengthCounter) = '\0';
+	
+	if(passwordLengthCounter>=passwordMaxLength){
+		printf("Password entered is too long. Aborting.\n");
+		exit(-1);
+	}
+	customer_t *ptr = &c;
+	bool loginSuccessful = loginCustomer(ptr);
+	if(loginSuccessful ) {
+		printf("Welcome to the menu!\n");
+		//call menu()
+	}else if(!loginSuccessful && attempts < MAX_LOGIN_ATTEMPTS){
+		printf("You have %d attempts left.\n", MAX_LOGIN_ATTEMPTS - attempts);
+		collectCustomerDataForLogin(++attempts);
+	}else{
+		printf("Maximum number of attempts reached. Program terminates.\n");
+		exit(-1);
+		//call error()
+	}
+	
+}
+
+bool loginCustomer(customer_t *c)
+{
+	bool foundCustomerEntryInFile = false;
+	char *searchForThisString = generateCheckString(c->ID,c->password);
+	char *lineFromCustomerFile = calloc(40,sizeof(char));
+	FILE *readCustomerFile = fopen("CustomerData.txt", "r");
+	if(readCustomerFile==NULL){
+		printf("Could not find file. Aborting.\n");
+		exit(-1);
+		//call error()
+	}
+	while((fscanf(readCustomerFile,"%s",lineFromCustomerFile)!=EOF)){
+			if(strcmp(searchForThisString,lineFromCustomerFile)==0){
+				foundCustomerEntryInFile = true;
+				break;
+			}
+	}
+	
+	if(checkLogin(foundCustomerEntryInFile)){
+		printf("Login successful.\n");
+		return foundCustomerEntryInFile;
+	}else{
+		printf("Login not successful.\n");
+	}
+	fclose(readCustomerFile);
+	return foundCustomerEntryInFile;
+}
+
+char *generateCheckString(char *ID, char *password){
+	int checkStringLength = strlen(ID) + 1 + strlen(password) + 1;
+	char *checkString = calloc(checkStringLength, sizeof(char));
+	checkString = strcat(ID,"=");
+	checkString = strcat(checkString,password);
+	*(checkString+checkStringLength) = '\0';
+	return checkString;
+}
diff --git a/src/LoginCustomer.h b/src/LoginCustomer.h
new file mode 100644
index 0000000..809765b
--- /dev/null
+++ b/src/LoginCustomer.h
@@ -0,0 +1,10 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include "CustomerProperties.h"
+#define MAX_LOGIN_ATTEMPTS 3
+char *generateCheckString(char *, char*);
+bool checkLogin(bool);
+void collectCustomerDataForLogin(int);
+bool loginCustomer(customer_t *);
diff --git a/src/_file_information.h b/src/_file_information.h
new file mode 100644
index 0000000..1cb5200
--- /dev/null
+++ b/src/_file_information.h
@@ -0,0 +1,2 @@
+#define MAX_LENGTH 100
+#define CUSTOMER_DATA_FILE "CustomerData.txt"
\ No newline at end of file
diff --git a/src/a.exe b/src/a.exe
new file mode 100644
index 0000000..7bbd2e2
Binary files /dev/null and b/src/a.exe differ
diff --git a/src/currentCustomerAccountBalance.c b/src/currentCustomerAccountBalance.c
new file mode 100644
index 0000000..a91e306
--- /dev/null
+++ b/src/currentCustomerAccountBalance.c
@@ -0,0 +1,63 @@
+#include "currentCustomerAccountBalance.h"
+
+float fetchBalanceFromBalanceString(char balance_String[MAX_LENGTH]) {
+    float balance = 0;
+    char *token = strtok(balance_String, "="); // separates string to two parts
+    while (token != NULL) {
+        if (atoi(token) != 0) {
+            balance = atof(token); // converts string to float
+            break;
+        }
+        token = strtok(NULL, "=");
+    }
+    return balance;
+}
+
+float readFileAndGetAvailableBalance(FILE *file, char stringID[MAX_LENGTH]) {
+    float balance = 0;
+    bool keep_reading = true;
+    char buffer[MAX_LENGTH];
+    char balance_String[MAX_LENGTH];
+
+    while(keep_reading) {
+        fgets(buffer, MAX_LENGTH, file);
+        if (feof(file)) {
+            keep_reading = false;
+        }
+        else if(strstr(buffer, stringID)) {
+            for (int i = 0; i < 4; i++) {
+                fgets(buffer, MAX_LENGTH, file);
+            }
+            strcpy(balance_String, buffer);
+            balance = fetchBalanceFromBalanceString(balance_String);
+            keep_reading = false;
+        }
+
+    }
+    return balance;
+}
+
+float getAvailableAccountBalance(int user_id) {
+    float availableBalance = 0;
+    char stringID[MAX_LENGTH] = "ID=";
+    char user_id_as_string[MAX_LENGTH];
+
+    sprintf(user_id_as_string, "%d", user_id); // converts user_id to string
+    strcat(stringID, user_id_as_string);
+    // Now stringID is "ID=user_id"
+
+    FILE *file = fopen(CUSTOMER_DATA_FILE, "r"); 
+    if(file == 0) {
+        printf("Error: customer data file cannot be opened!\n");
+        return 0;
+    }
+    else {
+        availableBalance = readFileAndGetAvailableBalance(file, stringID);
+    }
+
+    
+    fclose(file);
+    
+    return availableBalance;
+    
+}
\ No newline at end of file
diff --git a/src/currentCustomerAccountBalance.h b/src/currentCustomerAccountBalance.h
new file mode 100644
index 0000000..2795450
--- /dev/null
+++ b/src/currentCustomerAccountBalance.h
@@ -0,0 +1,10 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include "_file_information.h"
+
+float getAvailableAccountBalance(int user_id);
+float fetchBalanceFromBalanceString(char balance_String[MAX_LENGTH]);
+float readFileAndGetAvailableBalance(FILE *file, char stringID[MAX_LENGTH]);
\ No newline at end of file
diff --git a/src/lineReplacer.h b/src/lineReplacer.h
new file mode 100644
index 0000000..999855c
--- /dev/null
+++ b/src/lineReplacer.h
@@ -0,0 +1,6 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+void replaceLineInFile(const char* file_name, int line, const char* new_line); //replaces the line at "line" on the file "file_name", with the new line "new_line".
\ No newline at end of file
diff --git a/src/main.c b/src/main.c
index a6b9b24..3e233a1 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,6 +1,8 @@
 #include <stdio.h>
+#include"mainMenu.h"
 
-int main() {
-    
+int main()
+{
+    ageInput();	
     return 0;
-}
\ No newline at end of file
+}
diff --git a/src/mainMenu.c b/src/mainMenu.c
new file mode 100644
index 0000000..9bdfccb
--- /dev/null
+++ b/src/mainMenu.c
@@ -0,0 +1,93 @@
+
+#include"mainMenu.h"
+
+
+bool agePermission(int age){
+
+    if(age >= 18)
+    {
+
+       return true;
+
+    }
+
+    else
+    {
+
+       return false;
+
+    }
+
+}
+
+bool checkIfInteger(char* input){
+
+    char *end_pointer;
+
+    strtol(input, &end_pointer, 10);
+
+    if (end_pointer == input || *end_pointer != '\0')
+    {
+
+        return false;
+
+    }
+
+    else
+    {
+
+        return true;
+
+    }
+}
+
+void ageInput(){
+
+    char input[20];
+    char* input_pointer;
+
+    long age;
+
+    printf("\nPlease specify your age : ");
+    scanf("%s",input);
+
+    if (checkIfInteger(input) == true )
+    {
+        age = strtol(input,&input_pointer,10);
+
+        if(agePermission(age)== true)
+	{
+            printf("Access granted!\n\n\n\n");
+
+            showMenu();
+
+        }
+	else if(agePermission(age)== false)
+	{
+
+                  printf("You should be at least 18 years old to create a bank account!\n");
+
+        }
+    }
+
+    else
+    {
+
+                  printf("input invalid! try again!\n");
+
+    }
+
+}
+
+
+void showMenu(){
+
+    printf("\t\t\t\t\t\t\t  Welcome to Bank Manager!");
+    printf("\n\n\n\n\t\t\t\t\t\tPlease select one of the following functions!");
+    printf("\n\n\n\n\t\t\t\t\t\t      ->Login as an existing costumer.");
+    printf("\n\n\t\t\t\t\t\t        ->Register as a new costumer.");
+    printf("\n\n\t\t\t\t\t\t           ->Login as an Employee.");
+    printf("\n\n\t\t\t\t\t\t\t\t ->Exit.\n");
+    printf("\n\n\n\n\n Selection :\n");
+
+}
diff --git a/src/mainMenu.h b/src/mainMenu.h
new file mode 100644
index 0000000..f62dda9
--- /dev/null
+++ b/src/mainMenu.h
@@ -0,0 +1,15 @@
+#ifndef MAINMENU_H_
+#define MAINMENU_H_
+
+#include<stdio.h>
+#include<stdlib.h>
+#include<stdbool.h>
+#include<string.h>
+
+void showMenu();
+void ageInput();
+
+bool agePermission(int age);
+bool checkIfInteger(char* input);
+
+#endif
diff --git a/src/updateCustomerAccountBalance.c b/src/updateCustomerAccountBalance.c
new file mode 100644
index 0000000..6986e08
--- /dev/null
+++ b/src/updateCustomerAccountBalance.c
@@ -0,0 +1,84 @@
+#include "updateCustomerAccountBalance.h"
+#include "currentCustomerAccountBalance.c"
+#include "lineReplacer.h"
+
+void replaceLineInFile(const char* file_name, int line, const char* new_line){
+    FILE* file = fopen(file_name, "r");
+    if (file == NULL) {
+        printf("Error opening file!\n");
+        return;
+    }
+    char current_string[100];
+    int current_line = 1;
+    char *temp_file_name = calloc(8+1, sizeof(char));
+    temp_file_name = "temp.txt";
+    FILE* temp_file = fopen(temp_file_name, "w");
+    if (temp_file == NULL) {
+        printf("Error creating temp file!\n");
+        fclose(file);
+        return;
+    }
+    while (fgets(current_string, sizeof(current_string),file) != NULL) {
+        if (current_line == line) {
+            fprintf(temp_file, "%s\n", new_line);
+            //fputs("\n", temp_file);
+        } else {
+            fprintf(temp_file, "%s", current_string);
+        }
+        current_line++;
+    }
+    fclose(file);
+    fclose(temp_file);
+    if(remove(file_name)!=0){
+        printf("could not remove the original file!");
+    } // Remove the original file
+    if(rename(temp_file_name, file_name)!=0){
+        printf("could not rename!");
+    } // Rename the temp file to the original file
+}
+
+void replaceBalanceInString(float replacementBalance, int currentLine) {
+    char newBalanceLine[MAX_LENGTH] = "balance=";
+    char balance_as_string[MAX_LENGTH];
+    sprintf(balance_as_string, "%f", replacementBalance); //converts replacement balance to string
+    strcat(newBalanceLine, balance_as_string);
+    replaceLineInFile("CustomerData.txt",currentLine,newBalanceLine);
+}
+
+bool updateAvailableAccountBalance(int user_id, float newBalance){
+
+    bool keep_reading = true;
+
+    char *buffer = malloc(MAX_LENGTH * sizeof(char));
+    char *stringID = malloc(MAX_LENGTH * sizeof(char));
+    stringID = "ID=";
+    char *user_id_as_string =malloc(MAX_LENGTH * sizeof(char));
+    char *balance_String = malloc(MAX_LENGTH * sizeof(char));
+    int currentLine=0;
+
+    sprintf(user_id_as_string, "%d", user_id); // converts user_id to string
+    strcat(stringID, user_id_as_string);
+
+    FILE *file = fopen("CustomerData.txt", "r");
+    //printf(stringID);
+    while(keep_reading) {
+        fgets(buffer, MAX_LENGTH, file);
+        currentLine++;
+        if (feof(file)) {
+            keep_reading = false;
+        }
+        else if(strstr(buffer, stringID)) { //found the customer
+            fgets(buffer, MAX_LENGTH, file);
+            fgets(buffer, MAX_LENGTH, file);
+            fgets(buffer, MAX_LENGTH, file);
+            fgets(buffer, MAX_LENGTH, file);
+            strcpy(balance_String, buffer);
+            currentLine+=4;
+            keep_reading = false;
+        }
+
+    }
+    fclose(file);;
+    replaceBalanceInString(newBalance,currentLine);
+    return true;
+}
diff --git a/src/updateCustomerAccountBalance.h b/src/updateCustomerAccountBalance.h
new file mode 100644
index 0000000..29f5b75
--- /dev/null
+++ b/src/updateCustomerAccountBalance.h
@@ -0,0 +1,11 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define MAX_LENGTH 100
+
+
+bool updateAvailableAccountBalance(int user_id, float newBalance);
+
+void replaceBalanceInString(float replacementBalance, int currentLine);
diff --git a/tests/support/.gitkeep b/tests/support/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_updateCustomerAccountBalance.c b/tests/test_updateCustomerAccountBalance.c
new file mode 100644
index 0000000..add1299
--- /dev/null
+++ b/tests/test_updateCustomerAccountBalance.c
@@ -0,0 +1,34 @@
+#ifdef TEST
+
+#include "unity.h"
+
+#include "updateCustomerAccountBalance.h"
+
+void setUp(void)
+{
+}
+
+void tearDown(void)
+{
+}
+
+void test_updateAvailableAccountBalanceSuccess(void){
+
+	int id1 = 1234;
+	int id2 = 1327;
+	int id3 = 1666;
+
+	int newBalance1=500;
+	int newBalance2=800;
+	int newBalance3=700;
+
+	bool results1=updateAvailableAccountBalance(id1,newBalance1);
+	bool results2=updateAvailableAccountBalance(id2,newBalance2);
+	bool results3=updateAvailableAccountBalance(id3,newBalance3);
+
+	TEST_ASSERT_TRUE(results1);
+	TEST_ASSERT_TRUE(results2);
+	TEST_ASSERT_TRUE(results3);
+	
+}
+#endif