diff --git a/db.cpp b/db.cpp
new file mode 100644
index 0000000..0cf4220
--- /dev/null
+++ b/db.cpp
@@ -0,0 +1,143 @@
+#include "db.h"
+#include <sqlite3.h>
+#include <iostream>
+#include <fstream>
+
+sqlite3* db = nullptr;
+
+// --- Connexion / fermeture ---
+bool openDB(const std::string& filename) {
+    int rc = sqlite3_open(filename.c_str(), &db);
+    if(rc) {
+        std::cerr << "Impossible d'ouvrir la base : " << sqlite3_errmsg(db) << "\n";
+        return false;
+    }
+    return true;
+}
+
+void closeDB() {
+    if(db) sqlite3_close(db);
+}
+
+// --- Authentification ---
+int loginUser(const std::string& login, const std::string& password) {
+    sqlite3_stmt* stmt;
+    std::string sql = "SELECT id, role FROM users WHERE login=? AND password=?";
+    sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, nullptr);
+    sqlite3_bind_text(stmt, 1, login.c_str(), -1, SQLITE_STATIC);
+    sqlite3_bind_text(stmt, 2, password.c_str(), -1, SQLITE_STATIC);
+
+    int role = -1;
+    int rc = sqlite3_step(stmt);
+    if(rc == SQLITE_ROW) {
+        role = sqlite3_column_int(stmt, 1); // 0=ADMIN, 1=PROF, 2=STUDENT
+    }
+    sqlite3_finalize(stmt);
+    return role;
+}
+
+// --- Étudiants ---
+std::vector<Student> getAllStudents() {
+    std::vector<Student> list;
+    sqlite3_stmt* stmt;
+    std::string sql = "SELECT s.id, s.nom, n.note1, n.note2, n.note3 FROM students s JOIN notes n ON s.id=n.student_id";
+    sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, nullptr);
+
+    while(sqlite3_step(stmt) == SQLITE_ROW) {
+        Student s;
+        s.id = sqlite3_column_int(stmt, 0);
+        s.nom = reinterpret_cast<const char*>(sqlite3_column_text(stmt, 1));
+        s.notes[0] = sqlite3_column_int(stmt, 2);
+        s.notes[1] = sqlite3_column_int(stmt, 3);
+        s.notes[2] = sqlite3_column_int(stmt, 4);
+        list.push_back(s);
+    }
+    sqlite3_finalize(stmt);
+    return list;
+}
+
+Student getStudentByLogin(const std::string& login) {
+    Student s;
+    sqlite3_stmt* stmt;
+    std::string sql = "SELECT s.id, s.nom, n.note1, n.note2, n.note3 FROM students s JOIN notes n ON s.id=n.student_id WHERE s.nom=?";
+    sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, nullptr);
+    sqlite3_bind_text(stmt, 1, login.c_str(), -1, SQLITE_STATIC);
+
+    if(sqlite3_step(stmt) == SQLITE_ROW){
+        s.id = sqlite3_column_int(stmt, 0);
+        s.nom = reinterpret_cast<const char*>(sqlite3_column_text(stmt, 1));
+        s.notes[0] = sqlite3_column_int(stmt, 2);
+        s.notes[1] = sqlite3_column_int(stmt, 3);
+        s.notes[2] = sqlite3_column_int(stmt, 4);
+    }
+    sqlite3_finalize(stmt);
+    return s;
+}
+
+// --- Modifier une note ---
+bool updateNote(int studentId, int noteIndex, int newNote) {
+    std::string col = "note" + std::to_string(noteIndex+1);
+    std::string sql = "UPDATE notes SET " + col + "=? WHERE student_id=?";
+    sqlite3_stmt* stmt;
+    sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, nullptr);
+    sqlite3_bind_int(stmt, 1, newNote);
+    sqlite3_bind_int(stmt, 2, studentId);
+
+    int rc = sqlite3_step(stmt);
+    sqlite3_finalize(stmt);
+    return rc == SQLITE_DONE;
+}
+
+// --- Export / Import ---
+bool exportData(const std::string& filename, const std::string& role, const std::string& login) {
+    std::ofstream file(filename);
+    if(!file.is_open()) return false;
+
+    std::vector<Student> list;
+    if(role == "ADMIN" || role == "PROF") list = getAllStudents();
+    else list.push_back(getStudentByLogin(login));
+
+    for(auto& s : list){
+        file << s.nom << " " << s.notes[0] << " " << s.notes[1] << " " << s.notes[2] << "\n";
+    }
+    file.close();
+    return true;
+}
+
+bool importData(const std::string& filename, const std::string& role) {
+    if(role == "STUDENT") return false; // pas autorisé
+
+    std::ifstream file(filename);
+    if(!file.is_open()) return false;
+
+    std::string nom;
+    int n1,n2,n3;
+    while(file >> nom >> n1 >> n2 >> n3){
+        if(role == "ADMIN"){
+            // chercher étudiant
+            sqlite3_stmt* stmt;
+            std::string sql = "UPDATE notes SET note1=?, note2=?, note3=? WHERE student_id=(SELECT id FROM students WHERE nom=?)";
+            sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, nullptr);
+            sqlite3_bind_int(stmt, 1, n1);
+            sqlite3_bind_int(stmt, 2, n2);
+            sqlite3_bind_int(stmt, 3, n3);
+            sqlite3_bind_text(stmt, 4, nom.c_str(), -1, SQLITE_STATIC);
+            sqlite3_step(stmt);
+            sqlite3_finalize(stmt);
+        } else if(role == "PROF"){
+            // modification notes seulement
+            sqlite3_stmt* stmt;
+            std::string sql = "UPDATE notes SET note1=?, note2=?, note3=? WHERE student_id=(SELECT id FROM students WHERE nom=?)";
+            sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, nullptr);
+            sqlite3_bind_int(stmt, 1, n1);
+            sqlite3_bind_int(stmt, 2, n2);
+            sqlite3_bind_int(stmt, 3, n3);
+            sqlite3_bind_text(stmt, 4, nom.c_str(), -1, SQLITE_STATIC);
+            sqlite3_step(stmt);
+            sqlite3_finalize(stmt);
+        }
+    }
+
+    file.close();
+    return true;
+}
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