diff --git a/CreditManager.swift b/CreditManager.swift
new file mode 100644
index 0000000..3d9caa3
--- /dev/null
+++ b/CreditManager.swift
@@ -0,0 +1,267 @@
+//
+//  CreditManager.swift
+//  Git_ Exercise
+//
+//  Created by sei_dev on 12/19/22.
+//
+
+import Foundation
+
+/// creditManager의 DataFile 관련 정보들
+enum DataFile {
+    /// 데이터가 저장되고 로드하는 json 파일 이름
+    static let name = "data.json"
+    /// 파일이 저장될 Directory
+    static let directory: String = FileManager.default.currentDirectoryPath
+    static let pathString = DataFile.directory.appending(DataFile.name)
+    static var pathUrl: URL {
+        if #available(macOS 13.0, *) {
+            return URL(filePath: DataFile.directory.appending(DataFile.name))
+        } else {
+            return URL(fileURLWithPath: DataFile.directory.appending(DataFile.name))
+        }
+    }
+}
+
+final class CreditManager {
+    /// CreditManager - singleton
+    static let shared = CreditManager()
+    private init() { }
+    
+    /// CreditManager의 현재 status
+    private var status: Status = .start
+    /// CreditManager에 등록된 Student의 List
+    private var students = [Student]()
+    
+    /// 1. 저장된 데이터 로드
+    /// 2. 프로그램 상태에 맞는 info 메세지 출력
+    /// 3. input 처리 및 실행
+    /// 4. error발생 시 설명 출력
+    ///     - 종료 error 시 데이터 저장 및 프로그램 종료
+    func run() {
+        loadData()
+        while true {
+            do {
+                IOManager.writeMessage(status.infoMessage)
+                let input = try IOManager.getInput(isStartStatus: status == .start)
+                let parsedInput = try parse(input: input)
+                try doWith(parsedInput)
+            } catch {
+                IOManager.writeMessage(error.localizedDescription, type: .error)
+                switch error {
+                case CMError.quitProgram:
+                    saveData()
+                    return
+                default:
+                    status = .start
+                }
+            }
+        }
+    }
+    
+    /// status 별 input parse
+    private func parse(input: String) throws -> ParsedInput {
+        guard let parsedInput = status.parse(input: input) else {
+            throw status == .start ? CMError.invalidStartInput : IOError.wrongInput
+        }
+        return parsedInput
+    }
+    
+    
+    /// 입력과 상태에 따라 CreditManager 작동 분기
+    ///
+    /// - result Infomation이 있다면 출력한다
+    /// - 실행 후 credit manager의 status는 start로 변경
+    private func doWith(_ input: ParsedInput) throws {
+        do {
+            switch self.status {
+            case .start:
+                try start(input)
+                return
+            case .addStudent:
+                try add(student: input)
+            case .deleteStudent:
+                try delete(student: input)
+            case .addScore:
+                try add(score: input)
+            case .deleteScore:
+                try delete(score: input)
+            case .showScoreAverage:
+                try show(score: input)
+            case .exit:
+                return
+            }
+        } catch {
+            throw error
+        }
+        if let resInfo = status.resMessage(input: input) {
+            IOManager.writeMessage(resInfo, type: .reaction)
+        }
+        status = .start
+    }
+}
+
+//MARK: - Start
+
+extension CreditManager {
+    /// 입력에 따라 credit manager의 status 변경
+    private func start(_ input: ParsedInput) throws {
+        guard let nextStatus = input[0] as? Status else {
+            throw CMError.invalidStartInput
+        }
+        guard nextStatus != .exit else {
+            throw CMError.quitProgram
+        }
+        guard [Status.start, Status.addStudent].contains(nextStatus) || false == students.isEmpty else {
+            throw CMError.emptyStudents
+        }
+        self.status = nextStatus
+    }
+}
+
+//MARK: - AddStudent
+
+extension CreditManager {
+    /// 입력받은 학생을 students에 추가
+    ///
+    /// Error occurs when
+    /// - 입력받은 학생이 이미 존재
+    private func add(student input: ParsedInput) throws {
+        guard let name = input[0] as? String else {
+            throw IOError.wrongInput
+        }
+        guard false == exists(student: name) else {
+            throw CMError.studentAleadyExists(name: name)
+        }
+        let student = Student(name: name)
+        students.append(student)
+    }
+    
+    /// 학생이 등록되어 있다면 true
+    private func exists(student name: String) -> Bool {
+        return students.contains { $0.name == name }
+    }
+}
+
+//MARK: - Delete Student
+
+extension CreditManager {
+    /// 입력받은 학생을 students에서 삭제
+    ///
+    /// Error occurs when
+    /// - 등록된 학생이 0명
+    /// - 입력받은 학생이 존재하지 않음
+    private func delete(student input: ParsedInput) throws {
+        guard false == students.isEmpty  else {
+            throw CMError.emptyStudents
+        }
+        guard let name = input[0] as? String else {
+            throw IOError.wrongInput
+        }
+        guard exists(student: name) else {
+            throw CMError.studentNotFound(name: name)
+        }
+        students.removeAll { $0.name == name }
+    }
+}
+
+
+//MARK: - Add Score
+
+extension CreditManager {
+    /// 등록된 학생에 course, score 정보 추가
+    ///
+    /// Error occurs when
+    /// - 입력받은 학생이 존재하지 않음
+    private func add(score input: ParsedInput) throws {
+        guard let name = input[0] as? String,
+              let course = input[1] as? String,
+              let score = input[2] as? Score else {
+            throw IOError.wrongInput
+        }
+        guard let student = students.first(where: { $0.name == name}) else {
+            throw CMError.studentNotFound(name: name)
+        }
+        student.update(course: course, score: score)
+    }
+}
+
+//MARK: - Delete Score
+
+extension CreditManager {
+    /// 등록된 학생의 course 정보 삭제
+    ///
+    /// Error occurs when
+    /// - 입력받은 학생이 존재하지 않음
+    /// - 학생 정보에 해당 과목이 등록되어 있지 않음
+    private func delete(score input: ParsedInput) throws {
+        guard let name = input[0] as? String,
+              let course = input[1] as? String else {
+            throw IOError.wrongInput
+        }
+        guard let student = students.first(where: { $0.name == name}) else {
+            throw CMError.studentNotFound(name: name)
+        }
+        guard student.remove(course: course) != nil else {
+            throw CMError.courseNotFound(name: name, course: course)
+        }
+    }
+}
+
+//MARK: - Show Average Score
+
+extension CreditManager {
+    /// 등록된 학생의 전체 과목과 평점 확인
+    ///
+    /// Error occurs when
+    /// - 입력받은 학생이 존재하지 않음
+    /// - 학생 정보에 등록된 과목이 없음
+    private func show(score input: ParsedInput) throws {
+        guard let name = input[0] as? String else {
+            throw IOError.wrongInput
+        }
+        guard let student = students.first(where: { $0.name == name}) else {
+            throw CMError.studentNotFound(name: name)
+        }
+        guard false == student.scores.isEmpty else {
+            throw CMError.emptyCourse(name: name)
+        }
+        IOManager.writeMessage(student.allScoresDescription)
+    }
+}
+
+
+extension CreditManager {
+    /// students property를 json 파일에 저장
+    private func saveData() {
+        let encoder = JSONEncoder()
+        encoder.outputFormatting = .prettyPrinted
+        do {
+            let data = try encoder.encode(StudentList(students: students))
+            
+            if false == FileManager.default.fileExists(atPath: DataFile.pathString) {
+                FileManager.default.createFile(atPath: DataFile.pathString, contents: nil)
+            }
+            
+            try data.write(to: DataFile.pathUrl)
+            let names = students.map {$0.name}
+            
+            IOManager.writeMessage(Info.Data.saved(names: names), type: .reaction)
+        } catch {
+            IOManager.writeMessage(error.localizedDescription, type: .error)
+        }
+    }
+    
+    /// json 파일 데이터를 students property에 불러오기
+    private func loadData() {
+        guard let data = try? Data(contentsOf: DataFile.pathUrl),
+              let studentList = try? JSONDecoder().decode(StudentList.self, from: data) else {
+            IOManager.writeMessage(Info.Warning.failedToLoadData, type: .error)
+            return
+        }
+        students = studentList.students
+        
+        let names = students.map {$0.name}
+        IOManager.writeMessage(Info.Data.loaded(names: names), type: .reaction)
+    }
+}
diff --git a/Error.swift b/Error.swift
new file mode 100644
index 0000000..34f38f0
--- /dev/null
+++ b/Error.swift
@@ -0,0 +1,56 @@
+//
+//  Error.swift
+//  Git_ Exercise
+//
+//  Created by sei_dev on 12/19/22.
+//
+
+import Foundation
+
+//MARK: - CMError
+
+enum CMError: Error {
+    case invalidStartInput
+    case studentAleadyExists(name: String)
+    case studentNotFound(name: String)
+    case emptyCourse(name: String)
+    case courseNotFound(name: String, course:String)
+    case emptyStudents
+    case quitProgram
+}
+
+extension CMError: LocalizedError {
+    public var errorDescription: String? {
+        switch self {
+        case .invalidStartInput:
+            return "입력이 잘못되었습니다. 1~5 사이의 숫자 혹은 X를 입력해주세요."
+        case let .studentAleadyExists(name):
+            return "\(name): 이미 존재하는 학생입니다. 추가하지 않습니다."
+        case let .studentNotFound(name):
+            return "\(name) 학생을 찾지 못했습니다."
+        case let .courseNotFound(name, course):
+            return "\(name) - \(course): 등록되지 않은 과목입니다."
+        case let .emptyCourse(name):
+            return "\(name): 등록된 과목이 없습니다."
+        case .emptyStudents:
+            return "등록된 학생이 존재하지 않습니다."
+        case .quitProgram:
+            return "프로그램을 종료합니다..."
+        }
+    }
+}
+
+//MARK: - IOError
+
+enum IOError: Error {
+    case wrongInput
+}
+
+extension IOError: LocalizedError {
+    public var errorDescription: String? {
+        switch self {
+        case .wrongInput:
+            return "입력이 잘못되었습니다. 다시 확인해주세요."
+        }
+    }
+}
diff --git a/IOManager.swift b/IOManager.swift
new file mode 100644
index 0000000..d8ec114
--- /dev/null
+++ b/IOManager.swift
@@ -0,0 +1,44 @@
+//
+//  IOManager.swift
+//  Git_ Exercise
+//
+//  Created by sei_dev on 12/19/22.
+//
+
+import Foundation
+
+/// Console output type
+enum OutputType {
+    case information
+    case reaction
+    case error
+}
+
+enum IOManager {
+    static let nameRegex = "^[A-Za-z0-9_]+$"
+    
+    /// 사용자 입력 받기
+    static func getInput(isStartStatus: Bool) throws -> String {
+        guard let input = readLine(),
+              input != "" else {
+            throw isStartStatus ? CMError.invalidStartInput : IOError.wrongInput
+        }
+        return input
+    }
+    
+    static func checkValidity(of str: String) -> Bool {
+        return str.range(of: Self.nameRegex, options: .regularExpression, range: nil, locale: nil) != nil
+    }
+    
+    /// message 콘솔에 출력
+    static func writeMessage(_ message: String, type: OutputType = .information) {
+        switch type {
+        case .information:
+            print("> \(message)")
+        case .reaction:
+            print("< \(message)")
+        case .error:
+            fputs("⚠️ \(message)\n", stderr)
+        }
+    }
+}
diff --git a/Info.swift b/Info.swift
new file mode 100644
index 0000000..77bfaea
--- /dev/null
+++ b/Info.swift
@@ -0,0 +1,63 @@
+//
+//  Info.swift
+//  Git_ Exercise
+//
+//  Created by sei_dev on 12/19/22.
+//
+
+import Foundation
+
+enum Info {
+    static let start = """
+        원하는 기능을 입력해주세요.
+          1: 학생 추가, 2: 학생 삭제, 3: 성적 추가(변경), 4: 성적 삭제, 5: 평점 보기, X: 종료
+        """
+    enum Student {
+        static let forAdd = "추가할 학생의 이름을 입력해주세요."
+        static func added(name: String) -> String {
+            return "\(name) 학생을 추가했습니다."
+        }
+        static let forDelete = "삭제할 학생의 이름을 입력해주세요."
+        static func deleted(name: String) -> String {
+            return "\(name) 학생을 삭제했습니다."
+        }
+    }
+    enum Score {
+        static let forAdd = """
+            성적을 추가할 학생의 이름, 과목 이름, 성적(A+, A, F 등)을 띄어쓰기로 구분하여 차례로 작성해주세요.
+              입력 예) Mickey Swift A+
+              학생의 성적 중 해당 과목이 존재하면 기존 점수가 갱신됩니다.
+            """
+        static func added(name:String, course: String, score: String) -> String {
+                return "\(name) 학생의 \(course) 과목이 \(score)로 추가(변경)되었습니다."
+        }
+        static let forDelete = """
+            성적을 삭제할 학생의 이름, 과목 이름을 띄어쓰기로 구분하여 차례로 작성해주세요.
+              입력 예) Mickey Swift
+            """
+        static func deleted(name:String, course:String) -> String {
+            return "\(name) 학생의 \(course) 과목의 성적이 삭제되었습니다."
+        }
+        static let forAverage = "평점을 알고 싶은 학생의 이름을 입력해주세요."
+    }
+    enum Data {
+        static func saved(names: [String]) -> String {
+            return names.isEmpty ? "저장할 학생 정보가 없습니다."
+                : """
+                학생과 성적 정보를 성공적으로 저장했습니다.
+                저장된 학생: \(names.joined(separator: ", "))
+                """
+        }
+        static func loaded(names: [String]) -> String {
+            return """
+            학생과 성적 정보를 성공적으로 불러왔습니다.
+            불러온 학생: \(names.joined(separator: ", "))
+            """
+        }
+    }
+    
+    enum Warning {
+        static let failedToLoadData = "기존의 Data를 불러오는 데 실패했습니다."
+        static let failedToLoadReaction = "실행 결과 안내 메세지를 불러오는 데 실패했습니다."
+    }
+}
diff --git a/Score.swift b/Score.swift
new file mode 100644
index 0000000..ba572c4
--- /dev/null
+++ b/Score.swift
@@ -0,0 +1,68 @@
+//
+//  Score.swift
+//  Git_ Exercise
+//
+//  Created by sei_dev on 12/19/22.
+//
+
+import Foundation
+
+enum Score: Float, Codable {
+    case APlus = 4.5
+    case A = 4
+    case BPlus = 3.5
+    case B = 3
+    case CPlus = 2.5
+    case C = 2
+    case DPlus = 1.5
+    case D = 1
+    case F = 0
+    
+    var description: String {
+        switch self {
+        case .APlus:
+            return "A+"
+        case .A:
+            return "A0"
+        case .BPlus:
+            return "B+"
+        case .B:
+            return "B0"
+        case .CPlus:
+            return "C+"
+        case .C:
+            return "C0"
+        case .DPlus:
+            return "D+"
+        case .D:
+            return "D0"
+        case .F:
+            return "F"
+        }
+    }
+    
+    init?(score: String) {
+        switch score {
+        case "A+", "a+", "4.5":
+            self = .APlus
+        case "A", "a", "A0", "a0", "4", "4.0":
+            self = .A
+        case "B+", "b+", "3.5":
+            self = .BPlus
+        case "B", "b", "B0", "b0", "3", "3.0":
+            self = .B
+        case "C+", "c+", "2.5":
+            self = .CPlus
+        case "C", "c", "C0", "c0", "2", "2.0":
+            self = .C
+        case "D+", "d+", "1.5":
+            self = .DPlus
+        case "D", "d", "D0", "d0", "1", "1.0":
+            self = .D
+        case "F", "f", "0", "0.0":
+            self = .F
+        default:
+            return nil
+        }
+    }
+}
diff --git a/Status.swift b/Status.swift
new file mode 100644
index 0000000..5a332b1
--- /dev/null
+++ b/Status.swift
@@ -0,0 +1,114 @@
+//
+//  Status.swift
+//  Git_ Exercise
+//
+//  Created by sei_dev on 12/19/22.
+//
+
+import Foundation
+
+typealias ParsedInput = [Codable]
+
+/// status 정보
+enum Status: String, Codable {
+    case start = "0"
+    case addStudent = "1"
+    case deleteStudent = "2"
+    case addScore = "3"
+    case deleteScore = "4"
+    case showScoreAverage = "5"
+    case exit = "X"
+}
+
+//MARK: - Info Message
+
+extension Status {
+    var infoMessage: String {
+        switch self {
+        case .start:
+            return Info.start
+        case .addStudent:
+            return Info.Student.forAdd
+        case .deleteStudent:
+            return Info.Student.forDelete
+        case .addScore:
+            return Info.Score.forAdd
+        case .deleteScore:
+            return Info.Score.forDelete
+        case .showScoreAverage:
+            return Info.Score.forAverage
+        default:
+            return ""
+        }
+    }
+}
+
+//MARK: - Result Message
+
+extension Status {
+    func resMessage(input: ParsedInput) -> String? {
+        switch self {
+        case .addStudent:
+            if let name = input[0] as? String {
+                return Info.Student.added(name: name)
+            }
+        case .deleteStudent:
+            if let name = input[0] as? String {
+                return Info.Student.deleted(name: name)
+            }
+        case .addScore:
+            if let name = input[0] as? String,
+               let course = input[1] as? String,
+               let score = input[2] as? Score {
+                return Info.Score.added(name: name, course: course, score: score.description)
+            }
+        case .deleteScore:
+            if let name = input[0] as? String,
+               let course = input[1] as? String {
+                return Info.Score.deleted(name: name, course: course)
+            }
+        default:
+            return nil
+        }
+        return Info.Warning.failedToLoadReaction
+    }
+}
+
+//MARK: - Status - parse method
+
+extension Status {
+    /// status에 따라 사용자 입력 parse
+    func parse(input: String) -> ParsedInput? {
+        let splited = input.components(separatedBy: " ")
+        switch (self, splited.count) {
+        case (.start, 1):
+            guard let status = Status(rawValue: splited[0]) else {
+                return nil
+            }
+            return [status]
+        case (.addStudent, 1), (.deleteStudent, 1), (.showScoreAverage, 1):
+            guard IOManager.checkValidity(of: splited[0]) else {
+                return nil
+            }
+            return splited
+        case (.addScore, 3):
+            guard IOManager.checkValidity(of: splited[0]),
+                  IOManager.checkValidity(of: splited[1]),
+                  let score = Score(score: splited[2]) else {
+                return nil
+            }
+            var res = [Codable]()
+            res.append(contentsOf: splited)
+            res[2] = score
+            return res
+        case (.deleteScore, 2):
+            guard IOManager.checkValidity(of: splited[0]),
+                  IOManager.checkValidity(of: splited[1]) else {
+                return nil
+            }
+            return splited
+        default:
+            return nil
+        }
+    }
+}
diff --git a/Student.swift b/Student.swift
new file mode 100644
index 0000000..245d355
--- /dev/null
+++ b/Student.swift
@@ -0,0 +1,48 @@
+//
+//  Student.swift
+//  Git_ Exercise
+//
+//  Created by sei_dev on 12/19/22.
+//
+
+import Foundation
+
+final class Student: Codable {
+    let name: String
+    private(set) var scores = [String:Score]()
+    
+    var isCourseEmpty: Bool {
+        return scores.isEmpty
+    }
+    
+    var averageScore: Float {
+        let total = scores.values.reduce(0) { $0 + $1.rawValue }
+        return total/Float(scores.values.count)
+    }
+    
+    var allScoresDescription: String {
+        var res = ""
+        for item in scores {
+            res += "\(item.key): \(item.value.description)\n"
+        }
+        return res + "평점: " + String(format: "%.2f", averageScore)
+    }
+    
+    init(name: String) {
+        self.name = name
+    }
+    
+    func update(course: String, score: Score) {
+        scores.updateValue(score, forKey: course)
+    }
+    
+    func remove(course: String) -> Score? {
+        return scores.removeValue(forKey: course)
+    }
+}
+
+//MARK: - Student DataStructure
+
+struct StudentList: Codable {
+    let students: [Student]
+}
diff --git a/main.swift b/main.swift
new file mode 100644
index 0000000..11d507d
--- /dev/null
+++ b/main.swift
@@ -0,0 +1,11 @@
+//
+//  main.swift
+//  Git_ Exercise
+//
+//  Created by sei_dev on 2022/12/18.
+//
+
+import Foundation
+
+let cm = CreditManager.shared
+cm.run()