diff --git a/src/main/java/seedu/address/flashcard/CardId.java b/src/main/java/seedu/address/flashcard/CardId.java
new file mode 100644
index 00000000000..d0d49863ed3
--- /dev/null
+++ b/src/main/java/seedu/address/flashcard/CardId.java
@@ -0,0 +1,55 @@
+package seedu.address.flashcard;
+
+/**
+ * The unique identity number for each flash card.
+ * Guarantees: Each card's id number is unique.
+ */
+public class CardId {
+
+    // The id number for the next flash card generated.
+    private static int frontier = 0;
+    private final int identityNumber;
+
+    /**
+     * Constructor of the class, automatically generate a unique identity number.
+     */
+    public CardId() {
+        identityNumber = frontier;
+        frontier++;
+    }
+
+    public int getIdentityNumber() {
+        return identityNumber;
+    }
+
+    /**
+     * While finding a flashcard, compare that the id number of this card matches the search string or not.
+     * @param s The search parameter, target string.
+     * @return true if the id number indeed contains the target information, false otherwise.
+     */
+    public boolean contains(String s) {
+        String idAsString = Integer.toString(identityNumber);
+        return idAsString.contains(s);
+    }
+
+    @Override
+    public String toString() {
+        return Integer.toString(identityNumber);
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        if (other == this) {
+            return true;
+        }
+        if (!(other instanceof CardId)) {
+            return false;
+        }
+        return identityNumber == ((CardId) other).getIdentityNumber();
+    }
+
+    @Override
+    public int hashCode() {
+        return identityNumber;
+    }
+}
diff --git a/src/main/java/seedu/address/flashcard/Score.java b/src/main/java/seedu/address/flashcard/Score.java
new file mode 100644
index 00000000000..4f0bdc33530
--- /dev/null
+++ b/src/main/java/seedu/address/flashcard/Score.java
@@ -0,0 +1,52 @@
+package seedu.address.flashcard;
+
+/**
+ * The record of how many correct and wrong answers has the user done.
+ */
+public class Score {
+
+    private static final String MESSAGE_BEFORE_TOTAL = "Total number of practices: ";
+    private static final String MESSAGE_BEFORE_CORRECT = "Number of correct answers: ";
+    private static final String MESSAGE_BEFORE_WRONG = "Number of wrong answer: ";
+    private static final String MESSAGE_BEFORE_PERCENTAGE = "Total Correct rate: ";
+    private int correctAnswerNumber;
+    private int wrongAnswerNumber;
+
+    public Score() {
+        correctAnswerNumber = 0;
+        wrongAnswerNumber = 0;
+    }
+
+    public int getCorrectAnswerNumber() {
+        return correctAnswerNumber;
+    }
+
+    public int getWrongAnswerNumber() {
+        return wrongAnswerNumber;
+    }
+
+    public void addCorrectAnswerNumber() {
+        correctAnswerNumber++;
+    }
+
+    public void addWrongAnswerNumber() {
+        wrongAnswerNumber++;
+    }
+
+    public int getTotalAnswerNumber() {
+        return correctAnswerNumber + wrongAnswerNumber;
+    }
+
+    public float getCorrectRate() {
+        return correctAnswerNumber / getCorrectAnswerNumber();
+    }
+
+    @Override
+    public String toString() {
+        String totalMessage = MESSAGE_BEFORE_TOTAL + Integer.toString(getTotalAnswerNumber()) + "\n";
+        String correctMessage = MESSAGE_BEFORE_CORRECT + Integer.toString(getCorrectAnswerNumber()) + "\n";
+        String wrongMessage = MESSAGE_BEFORE_WRONG + Integer.toString(getWrongAnswerNumber()) + "\n";
+        String percentageMessage = MESSAGE_BEFORE_PERCENTAGE + Float.toString(getCorrectRate()) + "\n";
+        return totalMessage + correctMessage + wrongMessage + percentageMessage;
+    }
+}
diff --git a/src/main/java/seedu/address/flashcard/TimeLimit.java b/src/main/java/seedu/address/flashcard/TimeLimit.java
new file mode 100644
index 00000000000..760f94aae69
--- /dev/null
+++ b/src/main/java/seedu/address/flashcard/TimeLimit.java
@@ -0,0 +1,60 @@
+package seedu.address.flashcard;
+
+import static seedu.address.commons.util.AppUtil.checkArgument;
+
+/**
+ * The time limit for doing a quiz
+ * Guarantees: Does not exceed an hour, minutes and seconds are both between 0 and 60.
+ */
+public class TimeLimit {
+
+    private static final String MESSAGE_CONSTRAINTS = "Time limit must be in the format of two integers,"
+            + "representing minutes and seconds respectively. Since this a flashcard system, we do not "
+            + "support time limit more than or equals to an hour.";
+    private static final String MESSAGE_AFTER_MINUTES = " minutes ";
+    private static final String MESSAGE_AFTER_SECONDS = " seconds ";
+    private int minutes;
+    private int seconds;
+
+    // Default Time Limit, 1 minute.
+    public TimeLimit() {
+        minutes = 1;
+        seconds = 0;
+    }
+
+    public TimeLimit(int minutes, int seconds) {
+        checkArgument(isValidTimeLimit(minutes, seconds), MESSAGE_CONSTRAINTS);
+        this.minutes = minutes;
+        this.seconds = seconds;
+    }
+
+    /**
+     * Ensure both minutes and seconds are between 0 and 60
+     * The total time should be less than an hour
+     */
+    private boolean isValidTimeLimit(int minutes, int seconds) {
+        if (seconds < 0 || minutes < 0 || seconds >= 60 || minutes >= 60) {
+            return false;
+        }
+        return true;
+    }
+
+    @Override
+    public String toString() {
+        String minutesString = Integer.toString(minutes);
+        String secondsString = Integer.toString(seconds);
+        return minutesString + MESSAGE_AFTER_MINUTES + secondsString + MESSAGE_AFTER_SECONDS;
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        if (other == this) {
+            return true;
+        }
+        if (!(other instanceof TimeLimit)) {
+            return false;
+        }
+        return minutes == ((TimeLimit) other).minutes && seconds == ((TimeLimit) other).seconds;
+    }
+
+}
diff --git a/src/test/java/seedu/address/flashcard/CardIdTest.java b/src/test/java/seedu/address/flashcard/CardIdTest.java
new file mode 100644
index 00000000000..4242918fdbb
--- /dev/null
+++ b/src/test/java/seedu/address/flashcard/CardIdTest.java
@@ -0,0 +1,21 @@
+package seedu.address.flashcard;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class CardIdTest {
+
+    private CardId id1 = new CardId();
+    private CardId id2 = new CardId();
+    private CardId id3 = new CardId();
+    private CardId id4 = new CardId();
+
+    @Test
+    public void generateIdTest() {
+        assertEquals(0, id1.getIdentityNumber());
+        assertEquals(1, id2.getIdentityNumber());
+        assertEquals(2, id3.getIdentityNumber());
+        assertEquals(3, id4.getIdentityNumber());
+    }
+}