ElectiveCoursesIBU.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.18;

import "@openzeppelin/contracts/utils/Strings.sol";

contract ElectiveCoursesIBU {
    // Course mappings
    mapping(uint => uint) private courseCapacity;

    mapping(uint =>  mapping(address => bool)) private courseStudents;

    string[] private courses = [
        "Advanced Web3 Concepts", // 0
        "Introduction to DevOps", // 1
        "Secure Software System Development", // 2
        "Software Engineering", // 3
        "Introduction to Machine Learning", // 4
        "Introduction to Mobile and Wireless Networking", // 5
        "Human-Computer Interaction" // 6
    ];

    uint[] private maxCap = [
        35, 45, 75, 75, 105, 35, 40
    ];

    function getCourse(uint id) public view returns (string memory) {
        return courses[id];
    }

    function getCourseWithCapacity(uint id) public view returns (string memory) {
        return string.concat(courses[id], " (", Strings.toString(courseCapacity[id]), "/", Strings.toString(maxCap[id]), ")");
    }

    function registerCourses(address student, uint[] calldata courseIds) external {
        for (uint i = 0; i < courseIds.length; i++) {
            // Check max capacity for a course
            require(courseIds[i] >= 0 && courseIds[i] <= 6, "You are choosing a non-existing course!");
            require(courseCapacity[courseIds[i]] < maxCap[courseIds[i]], string.concat("Course ", getCourse(courseIds[i]), " filled up!"));
            require(courseStudents[courseIds[i]][student] != true, string.concat("You already chose ", getCourse(courseIds[i]), "!"));

            courseCapacity[courseIds[i]]++;
            courseStudents[courseIds[i]][student] = true;
        }
    }

    function unregisterCourses(address student, uint[] calldata courseIds) external {
        for (uint i = 0; i < courseIds.length; i++) {
            // Check max capacity for a course
            require(courseIds[i] >= 0 && courseIds[i] <= 6, "You are selecting a non-existing course!");
            require(courseStudents[courseIds[i]][student] == true, string.concat("You are not enrolled to ", getCourse(courseIds[i]), "!"));

            courseCapacity[courseIds[i]]--;
            courseStudents[courseIds[i]][student] = false;
        }
    }

    function getStudentCourses(address student) external view returns (string[] memory) {
        uint size = 0;
        for (uint i = 0; i < 7; i++) {
            if (courseStudents[i][student] == true) {
                size++;
            }
        }

        string[] memory sc = new string[](size);
        uint count = 0;
        for (uint i = 0; i < 7; i++) {
            if (courseStudents[i][student] == true) {
                sc[count] = getCourse(i);
                count++;
            }
        }
        return sc;
    }
}