# MIPS Assembly: Attendance System (Command-Line Version)
#
# This program implements a simple command-line attendance tracking system.
# It allows a user to view attendance records and mark students as
# present, absent, or late.
#
# This version is compatible with most online MIPS simulators.

.data
    # --- Constants for Attendance Status ---
    PRESENT: .word 1         # Represents 'Present' status
    ABSENT:  .word 2         # Represents 'Absent' status
    LATE:    .word 3         # Represents 'Late' status

    # --- Student Data Structure ---
    # We will use parallel arrays to store student information.
    # student_ids: An array of words to store unique student IDs.
    # student_status: An array of words to store the attendance status for each student.
    # The student at index `i` in `student_ids` has their status at index `i` in `student_status`.

    student_ids:    .word 101, 102, 103, 104, 105, 106, 107, 108, 109, 110 # Example student IDs
    student_status: .word 0, 0, 0, 0, 0, 0, 0, 0, 0, 0   # Initial status (0 for 'Not Marked')
    STUDENT_COUNT:  .word 10                                    # Total number of students

    # --- User Interface Strings ---
    welcome_msg: .asciiz "\n*** MIPS Attendance Management System ***\n"
    menu: .asciiz "\nPlease select an option:\n  1. Mark Attendance\n  2. View Attendance Sheet\n  3. Exit\n\nYour choice: "
    prompt_student_id: .asciiz "Enter Student ID to mark: "
    prompt_status: .asciiz "Enter status (1=Present, 2=Absent, 3=Late): "
    invalid_choice_msg: .asciiz "Error: Invalid choice. Please try again.\n"
    invalid_id_msg: .asciiz "Error: Student ID not found.\n"
    invalid_status_msg: .asciiz "Error: Invalid status code.\n"
    update_success_msg: .asciiz "Attendance marked successfully!\n"
    exit_msg: .asciiz "\nExiting the program. Goodbye!\n"
    sheet_header: .asciiz "\n--- Attendance Sheet ---\n"
    student_id_label: .asciiz "Student ID: "
    status_label: .asciiz "  |  Status: "
    status_not_marked: .asciiz "Not Marked\n"
    status_present: .asciiz "Present\n"
    status_absent: .asciiz "Absent\n"
    status_late: .asciiz "Late\n"
    newline: .asciiz "\n"

.text
.globl main

#-----------------------------------------------------------------------
# main: The main entry point of the program.
# Displays the main menu and directs the user based on their choice.
#-----------------------------------------------------------------------
main:
    # Display welcome message
    li $v0, 4
    la $a0, welcome_msg
    syscall

main_loop:
    # Display the menu
    li $v0, 4
    la $a0, menu
    syscall

    # Get user's choice
    li $v0, 5
    syscall
    move $t0, $v0 # Store user's choice in $t0

    # Branch based on user choice
    beq $t0, 1, mark_attendance_section # Option 1: Mark Attendance
    beq $t0, 2, view_attendance_section # Option 2: View Attendance
    beq $t0, 3, exit_program           # Option 3: Exit

    # Handle invalid choice
    li $v0, 4
    la $a0, invalid_choice_msg
    syscall
    j main_loop

#-----------------------------------------------------------------------
# mark_attendance_section: Handles the logic for marking a student's attendance.
# Prompts for student ID and desired status, then updates the record.
#-----------------------------------------------------------------------
mark_attendance_section:
    # Prompt for Student ID
    li $v0, 4
    la $a0, prompt_student_id
    syscall
    li $v0, 5
    syscall
    move $s0, $v0 # Store the target student ID in $s0

    # Prompt for Status
    li $v0, 4
    la $a0, prompt_status
    syscall
    li $v0, 5
    syscall
    move $s1, $v0 # Store the desired status in $s1

    # --- Validate the status code ---
    lw $t1, PRESENT
    lw $t2, ABSENT
    lw $t3, LATE
    beq $s1, $t1, find_student # Status is Present
    beq $s1, $t2, find_student # Status is Absent
    beq $s1, $t3, find_student # Status is Late

    # If status is not 1, 2, or 3, it's invalid
    li $v0, 4
    la $a0, invalid_status_msg
    syscall
    j main_loop

find_student:
    # --- Find the student's index ---
    la $t0, student_ids   # $t0 = address of student_ids array
    lw $t1, STUDENT_COUNT # $t1 = number of students
    li $t2, 0             # $t2 = loop counter (i)

find_loop:
    beq $t2, $t1, student_not_found # If i == STUDENT_COUNT, student not found

    # Load the current student ID from the array
    lw $t3, 0($t0) # $t3 = student_ids[i]

    # Check if it matches the target ID
    beq $t3, $s0, student_found # If student_ids[i] == target_id, we found it

    # Move to the next student
    addi $t0, $t0, 4 # Move to the next element in student_ids
    addi $t2, $t2, 1 # i++
    j find_loop

student_not_found:
    li $v0, 4
    la $a0, invalid_id_msg
    syscall
    j main_loop

student_found:
    # $t2 now holds the index of the student
    # Update the corresponding status in student_status array

    # Calculate the address of student_status[i]
    la $t4, student_status # $t4 = base address of student_status
    sll $t5, $t2, 2        # $t5 = i * 4 (offset)
    add $t4, $t4, $t5      # $t4 = address of student_status[i]

    # Store the new status
    sw $s1, 0($t4) # student_status[i] = new_status

    # Display success message
    li $v0, 4
    la $a0, update_success_msg
    syscall
    j main_loop

#-----------------------------------------------------------------------
# view_attendance_section: Displays the full attendance sheet.
# Iterates through all students and prints their ID and current status.
#-----------------------------------------------------------------------
view_attendance_section:
    # Print header
    li $v0, 4
    la $a0, sheet_header
    syscall

    # Initialize loop variables
    la $t0, student_ids     # $t0 = address of student_ids
    la $t1, student_status  # $t1 = address of student_status
    lw $t2, STUDENT_COUNT   # $t2 = number of students
    li $t3, 0               # $t3 = loop counter (i)

view_loop:
    beq $t3, $t2, view_loop_end # If i == STUDENT_COUNT, end loop

    # --- Print "Student ID: " ---
    li $v0, 4
    la $a0, student_id_label
    syscall

    # --- Print the student ID ---
    li $v0, 1
    lw $a0, 0($t0) # Load student_ids[i]
    syscall

    # --- Print " | Status: " ---
    li $v0, 4
    la $a0, status_label
    syscall

    # --- Print the status string ---
    lw $t4, 0($t1) # Load student_status[i] into $t4

    # Load status constants for comparison
    lw $t5, PRESENT
    lw $t6, ABSENT
    lw $t7, LATE

    beq $t4, $t5, print_present
    beq $t4, $t6, print_absent
    beq $t4, $t7, print_late

    # Default case: Status not marked
    li $v0, 4
    la $a0, status_not_marked
    syscall
    j next_student

print_present:
    li $v0, 4
    la $a0, status_present
    syscall
    j next_student

print_absent:
    li $v0, 4
    la $a0, status_absent
    syscall
    j next_student

print_late:
    li $v0, 4
    la $a0, status_late
    syscall
    j next_student

next_student:
    # Move to the next student in both arrays
    addi $t0, $t0, 4 # Next ID
    addi $t1, $t1, 4 # Next status
    addi $t3, $t3, 1 # i++
    j view_loop

view_loop_end:
    j main_loop

#-----------------------------------------------------------------------
# exit_program: Terminates the program execution.
#-----------------------------------------------------------------------
exit_program:
    # Print exit message
    li $v0, 4
    la $a0, exit_msg
    syscall

    # Terminate the program
    li $v0, 10
    syscall