Add Grade class with letter/GPA conversion and averaging

Author: Adi-Sin101

src/Features/Grade.java

@@ -0,0 +1,46 @@
+public class Grade {
+
+    // Simple numeric -> letter grade
+    public String toLetter(double score) {
+        if (score < 0 || score > 100) {
+            throw new IllegalArgumentException("Score must be 0..100");
+        }
+        if (score >= 90) return "A";
+        if (score >= 80) return "B";
+        if (score >= 70) return "C";
+        if (score >= 60) return "D";
+        return "F";
+    }
+
+    // GPA points (typical 4.0 scale)
+    public double toGpaPoints(double score) {
+        String letter = toLetter(score);
+        switch (letter) {
+            case "A": return 4.0;
+            case "B": return 3.0;
+            case "C": return 2.0;
+            case "D": return 1.0;
+            default:  return 0.0;
+        }
+    }
+
+    // Average of array
+    public double average(double[] scores) {
+        if (scores == null || scores.length == 0) {
+            throw new IllegalArgumentException("Scores required");
+        }
+        double sum = 0;
+        for (double s : scores) {
+            if (s < 0 || s > 100) {
+                throw new IllegalArgumentException("Score out of range: " + s);
+            }
+            sum += s;
+        }
+        return sum / scores.length;
+    }
+
+    // Average letter
+    public String averageLetter(double[] scores) {
+        return toLetter(average(scores));
+    }
+}