student_mng.java

import java.util.*;

class Student {
    int roll, s_mark1, s_mark2, s_mark3;
    String name, sub1, sub2, sub3;
    int avg, total;

    void setName() {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter Student Name: ");
        name = sc.nextLine();
    }

    String getName() {
        return name;
    }

    void showName() {
        System.out.println("Student Name: " + name);
    }

    void setRoll() {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter Roll No: ");
        roll = sc.nextInt();
    }

    int getRoll() {
        return roll;
    }

    void showRoll() {
        System.out.println("Roll no: " + roll);
    }

    void setSub() {
        if (!(sub1 == null)) {
            System.out.println("Subject already Entered");
            return;
        }
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter Subject 1 Name: ");
        sub1 = sc.nextLine();
        System.out.print("Enter Subject 2 Name: ");
        sub2 = sc.nextLine();
        System.out.print("Enter Subject 3 Name: ");
        sub3 = sc.nextLine();
    }

    void getSub() {
        if (sub1 == null) {
            System.out.println("Please enter Subject Name");
            return;
        }
        System.out.println("Subject 1 Name: " + sub1);
        System.out.println("Subject 2 Name: " + sub2);
        System.out.println("Subject 3 Name: " + sub3);
    }

    void setMark() {
        if (!(s_mark1 == 0)) {
            System.out.println("Marks already Entered");
            return;
        }
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter Subject 1 Marks: ");
        s_mark1 = sc.nextInt();
        System.out.print("Enter Subject 2 Marks: ");
        s_mark2 = sc.nextInt();
        System.out.print("Enter Subject 3 Marks: ");
        s_mark3 = sc.nextInt();
    }

    void getMark() {
        if (s_mark1 == 0) {
            System.out.println("Please enter Marks");
            return;
        }
        System.out.println("Subject 1 Marks" + s_mark1);
        System.out.println("Subject 2 Marks" + s_mark2);
        System.out.println("Subject 3 Marks" + s_mark3);
    }

    void getTotal() {
        total = s_mark1 + s_mark2 + s_mark3;
        System.out.println("Total Marks: " + total);
    }

    void getAvg() {
        avg = (s_mark1 + s_mark2 + s_mark3) / 3;
        System.out.println("Average: " + avg);
    }

    void getGrade(){
        int mark=(s_mark1 + s_mark2 + s_mark3) / 3;
        if(mark>90){
            System.out.println("Grade: A+");
        }else if(mark>80){
            System.out.println("Grade: A");
        }else if(mark>70){
            System.out.println("Grade: B");
        }else if(mark>60){
            System.out.println("Grade: C");
        }else if(mark>50){
            System.out.println("Grade: D");
        }else{
            System.out.println("Grade: F");
        }
    }
    void show() {
        if (getStatus() == 0) {
            System.out.println("No data Found");
            return;
        }
        showRoll();
        showName();
        System.out.println(sub1 + ": " + s_mark1);
        System.out.println(sub2 + ": " + s_mark2);
        System.out.println(sub3 + ": " + s_mark3);
        getTotal();
        getAvg();
        getGrade();
    }

    int getStatus() {
        if (sub1 == null || s_mark1 == 0) {
            return 0;
        } else {
            return 1;
        }
    }
}

class student_mng {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Student arr[];
        int st, ch;
        System.out.print("Enter number of Students: ");
        st = sc.nextInt();
        arr = new Student[st];
        for (int i = 0; i < st; i++) {
            arr[i] = new Student();
            arr[i].setRoll();
            arr[i].setName();
        }
        do {
            System.out.println("===----------------Student Management---------------===");
            System.out.println("1.Show Individual Student");
            System.out.println("2.Enter Subject Name");
            System.out.println("3.Enter Subject Marks");
            System.out.println("4.Student Report");
            System.out.println("5.Update Student Details");
            System.out.println("6.Exit");
            System.out.print("Enter Your Choice: ");
            ch = sc.nextInt();
            int ck, temp = 0;
            switch (ch) {
                case 1:
                    temp = 0;
                    for (int i = 0; i < st; i++) {
                        System.out.println(arr[i].getRoll() + ". " + arr[i].getName());
                    }
                    System.out.print("Enter Roll no: ");
                    ck = sc.nextInt();
                    for (int i = 0; i < st; i++) {
                        if (arr[i].getRoll() == ck) {
                            arr[i].show();
                            temp = 1;
                            break;
                        }
                    }
                    if (temp == 0) {
                        System.out.println("Invalid Roll no!!");
                    }
                    break;
                case 2:
                    temp = 0;
                    for (int i = 0; i < st; i++) {
                        System.out.println(arr[i].getRoll() + ". " + arr[i].getName());
                    }
                    System.out.print("Enter Roll no: ");
                    ck = sc.nextInt();
                    for (int i = 0; i < st; i++) {
                        if (arr[i].getRoll() == ck) {
                            temp = 1;
                            arr[i].setSub();
                            break;
                        }
                    }
                    if (temp == 0) {
                        System.out.println("Invalid Roll no!!");
                    }
                    break;
                case 3:
                    temp = 0;
                    for (int i = 0; i < st; i++) {
                        System.out.println(arr[i].getRoll() + ". " + arr[i].getName());
                    }
                    System.out.print("Enter Roll no: ");
                    ck = sc.nextInt();
                    for (int i = 0; i < st; i++) {
                        if (arr[i].getRoll() == ck) {
                            temp = 1;
                            arr[i].setMark();
                            break;
                        }
                    }
                    if (temp == 0) {
                        System.out.println("Invalid Roll no!!");
                    }
                    break;
                case 4:
                    temp = 0;
                    for (int i = 0; i < st; i++) {
                        if (arr[i].getStatus() == 0) {
                            temp = 1;
                            System.out.println("Please Fill " + arr[i].getName() + "'s Data..");
                            break;
                        }
                    }
                    if (temp == 0) {
                        System.out.println("-------Student Report-------");
                        for (Student s : arr) {
                            s.show();
                            System.out.println(' ');
                        }
                    }
                    break;
                case 5:
                    temp = 0;
                    for (int i = 0; i < st; i++) {
                        System.out.println(arr[i].getRoll() + ". " + arr[i].getName());
                    }
                    System.out.print("Enter Roll no: ");
                    ck = sc.nextInt();
                    for (int i = 0; i < st; i++) {
                        if (arr[i].getRoll() == ck) {
                            temp=1;
                            int ich;
                            do {
                                System.out.println("1. Update Name");
                                System.out.println("2. Update Subject Names");
                                System.out.println("3. Update Subject Marks");
                                System.out.println("4. Back");
                                System.out.print("Enter Your Choice: ");
                                ich = sc.nextInt();
                                switch (ich) {
                                    case 1:
                                        arr[i].setName();
                                        break;
                                    case 2:
                                        arr[i].setSub();
                                        break;
                                    case 3:
                                        arr[i].setMark();
                                        break;
                                    case 4:
                                        break;
                                    default:
                                        System.out.println("Invalid Input");
                                        break;
                                }
                            } while (ich != 4);
                            break;
                        }
                    }
                    if (temp == 0) {
                        System.out.println("Invalid Roll no!!");
                    }
                    break;
                case 6:
                    System.out.println("Thank you for using RDS code, Have a Great Day");
                    break;
                default:
                    System.out.println("Invalid Choice, Try again..");
                    break;
            }
        } while (ch != 6);
    }
}