Object Oriented Programming & Methodology (CS-305) Notes

How unit 5 is examined

This unit covers C++ strings, exception handling, multithreading with STL collections, and the library/ATM case study; exception handling, multithreading with collections, and the library diagram carry the marks.

Strings

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Low weight</span>

Definition. <mark>A string is a sequence of characters; in C it is a char array ended by the null character '\0', and in C++ the std::string class (header <string>) manages such a sequence with member functions.</mark>

Key points.

A C-style string such as char s[] = "RGPV"; occupies one extra byte for '\0', so it needs 5 bytes.
std::string grows automatically, so the programmer does not manage size or memory.
length() or size() returns the number of characters, and append() or + joins two strings.
substr(pos, len) extracts a part, find(str) returns the first index or string::npos, and compare() returns 0 if equal, negative or positive otherwise.
C functions from <cstring> are strlen, strcpy, strcat and strcmp.

Example.

string s = "Object"; s.append(" Oriented");
cout << s.length();      // 15
cout << s.substr(0, 6);  // Object
cout << s.find("Ori");   // 7
cout << s.compare("Object"); // > 0

Asked: [7 marks] (Nov 2022) What is String? Explain functions of strings with suitable examples.

Exceptional handling

Definition. <mark>An exception is an abnormal runtime condition, such as division by zero or a failed allocation, that disrupts normal program flow; exception handling is the C++ mechanism of try, throw and catch that detects and handles it gracefully.</mark>

Diagram. <figure class="ds-fig" style="margin:1.4rem 0;overflow-x:auto"><svg xmlns="http://www.w3.org/2000/svg" id="dsfig-u5-01" viewBox="0 0 467 252" width="467" height="252" role="img" aria-label="try block (T), throw (Th), matching catch (C), normal continuation (N), program continues (E)"><style>#dsfig-u5-01 .e{stroke:#454C5A;stroke-width:1.4;fill:none}#dsfig-u5-01 .e.hi{stroke:#2340B8;stroke-width:2.6}#dsfig-u5-01 .n{fill:#FFFFFF;stroke:#16181D;stroke-width:1.4}#dsfig-u5-01 .n.hi{fill:#E3E9FC;stroke:#2340B8;stroke-width:2.2}#dsfig-u5-01 .n.rb-b{fill:#16181D;stroke:#16181D}#dsfig-u5-01 .n.rb-r{fill:#BD3227;stroke:#BD3227}#dsfig-u5-01 text{font-family:"JetBrains Mono",ui-monospace,Menlo,Consolas,monospace;font-size:13px}#dsfig-u5-01 .t{fill:#16181D;font-weight:500}#dsfig-u5-01 .t.inv{fill:#FFFFFF;font-weight:700}#dsfig-u5-01 .kd{stroke:#16181D;stroke-width:1.2}#dsfig-u5-01 .dot{fill:#16181D}#dsfig-u5-01 .ann{fill:#2340B8;font-size:11px;font-weight:700}#dsfig-u5-01 .lbl{fill:#6F7787;font-family:system-ui,-apple-system,sans-serif;font-size:12px;font-weight:700}#dsfig-u5-01 .ptr{fill:#2340B8;font-size:12px;font-weight:700}#dsfig-u5-01 .ah{fill:#454C5A}#dsfig-u5-01 .ah.hi{fill:#2340B8}#dsfig-u5-01 .wl rect{fill:#FFFFFF;stroke:#DCE0E7}#dsfig-u5-01 .wl .t{font-size:12px;font-weight:700}#dsfig-u5-01 .wl.hi rect{fill:#2340B8;stroke:#2340B8}#dsfig-u5-01 .wl.hi .t{fill:#FFFFFF}html.dark #dsfig-u5-01 .e{stroke:#B1B7C3}html.dark #dsfig-u5-01 .e.hi{stroke:#8FA3FF}html.dark #dsfig-u5-01 .n{fill:#161920;stroke:#E6E8ED}html.dark #dsfig-u5-01 .n.hi{fill:#1E2748;stroke:#8FA3FF}html.dark #dsfig-u5-01 .n.rb-b{fill:#E6E8ED;stroke:#E6E8ED}html.dark #dsfig-u5-01 .n.rb-r{fill:#FF7E71;stroke:#FF7E71}html.dark #dsfig-u5-01 .t{fill:#E6E8ED}html.dark #dsfig-u5-01 .t.inv{fill:#0F1115}html.dark #dsfig-u5-01 .kd{stroke:#E6E8ED}html.dark #dsfig-u5-01 .dot{fill:#E6E8ED}html.dark #dsfig-u5-01 .ann{fill:#8FA3FF}html.dark #dsfig-u5-01 .lbl{fill:#858D9C}html.dark #dsfig-u5-01 .ptr{fill:#8FA3FF}html.dark #dsfig-u5-01 .ah{fill:#B1B7C3}html.dark #dsfig-u5-01 .ah.hi{fill:#8FA3FF}html.dark #dsfig-u5-01 .wl rect{fill:#161920;stroke:#2A2E37}html.dark #dsfig-u5-01 .wl.hi rect{fill:#8FA3FF;stroke:#8FA3FF}html.dark #dsfig-u5-01 .wl.hi .t{fill:#0F1115}</style><defs><marker id="ah11" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="ah" d="M0,1 L9,5 L0,9 z"/></marker><marker id="ahh11" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="ah hi" d="M0,1 L9,5 L0,9 z"/></marker></defs><path class="e" d="M59,126 L148,126" marker-end="url(#ah11)"/><path class="e" d="M184.8,115.5 L280.5,51.6" marker-end="url(#ah11)"/><path class="e" d="M58,132 L278.1,205.4" marker-end="url(#ah11)"/><path class="e" d="M313.8,50.5 L409.5,114.4" marker-end="url(#ah11)"/><path class="e" d="M313.8,201.5 L409.5,137.6" marker-end="url(#ah11)"/><g class="wl"><rect x="81" y="117" width="47.1" height="18" rx="9"/><text class="t" x="104.5" y="126" dy=".35em" text-anchor="middle">error</text></g><g class="wl"><rect x="210" y="74" width="47.1" height="18" rx="9"/><text class="t" x="233.5" y="83" dy=".35em" text-anchor="middle">match</text></g><g class="wl"><rect x="138.3" y="160" width="61.5" height="18" rx="9"/><text class="t" x="169" y="169" dy=".35em" text-anchor="middle">noerror</text></g><circle class="n" cx="40" cy="126" r="18"/><text class="t" x="40" y="126" dy=".35em" text-anchor="middle">T</text><circle class="n" cx="169" cy="126" r="18"/><text class="t" x="169" y="126" dy=".35em" text-anchor="middle">Th</text><circle class="n" cx="298" cy="40" r="18"/><text class="t" x="298" y="40" dy=".35em" text-anchor="middle">C</text><circle class="n" cx="298" cy="212" r="18"/><text class="t" x="298" y="212" dy=".35em" text-anchor="middle">N</text><circle class="n" cx="427" cy="126" r="18"/><text class="t" x="427" y="126" dy=".35em" text-anchor="middle">E</text></svg><figcaption style="font-size:.82em;opacity:.72;margin-top:.45rem">try block (T), throw (Th), matching catch (C), normal continuation (N), program continues (E)</figcaption></figure>

Key points.

The try block encloses the code that may cause an error and is monitored for exceptions.
The throw statement raises an exception by giving a value (int, string or object) and transfers control out of the try block.
The catch block, placed immediately after try, receives the thrown value; the block whose parameter type matches is executed.
If no exception occurs, all catch blocks are skipped; if none matches, terminate() is called and the program aborts.
catch(...) is a catch-all handler and should be written last.
Several catch blocks may follow one try block, one per exception type.
Standard exceptions in <exception> include bad_alloc, out_of_range, invalid_argument and bad_cast, all with what().
Compared with error codes, exceptions separate error handling from normal logic and cannot be silently ignored.

Example. Array index out of bounds (index outside 0..n-1) and null pointer dereference are runtime errors; C++ arrays do not check, so vector::at() throws out_of_range, while a null pointer is tested and thrown by the programmer.

Program (Jun 2023).

int main() {
  int x, y, z; cin >> x >> y >> z;
  try {
    if (x - y == 0) throw "Division by zero";
    cout << "R = " << (float)z / (x - y);
  }
  catch (const char* m) { cout << "Error: " << m; }
}
// input 5 5 9 -> Error: Division by zero ; input 2 5 9 -> R = -3

Answer frame. Open with the definition of exception; draw the try-throw-catch flow; explain try, throw, catch in order, then matching, catch(...), standard exceptions and advantage over error codes; give the divide-by-zero program; close with one line on graceful termination. For the Jun 2023 program, define exception in two lines, then give the code and the two outputs.

Pitfall: Writing throw outside a try block, or a catch of the wrong type, aborts the program instead of handling the error.

Asked: [7 marks] (Nov 2019) Explain the concept of exception handling in C++ with an example. Asked: [7 marks] (May 2019) How exception are handled in C++ programming? Explain. Asked: [7 marks] (Dec 2020) What is meant by exceptions? How an exception is handled? Asked: [7 marks] (Jun 2020) What are exceptions and how are they handled? What are Array Index Out of Bounds and Null Pointer exceptions? Uses of try, catch and throw with example. Asked: [7 marks] (Dec 2023) What do you mean by exception? How is exception handled in C++? Explain with an example. Asked: [7 marks] (Jun 2023) What is exception? Write a program to read x, y, z and evaluate R = z / (x - y), throwing an exception on division by zero. Asked: [7 marks] (Nov 2022, Dec 2025) Explain exception handling and multithreading. Asked: [14 marks] (Nov 2018) Explain Exception Handling and multi-threading.

Multi-threading and Data collections

Definition. <mark>Multithreading is the concurrent execution of two or more threads, the smallest units of execution, within a single process; a collection is an object that stores and manages a group of elements, and a collection class is the class providing it, such as the STL vector, list, set and map.</mark>

Thread lifecycle. New, Runnable, Running, Waiting or Blocked, Terminated.

Key points.

A thread shares the code, data and heap of its process but has its own stack and registers, so it is lighter than a process.
Multithreading gives better CPU utilization because while one thread waits for input or output another runs.
It keeps applications responsive, since a GUI thread stays alive while a worker thread does a long job.
Threads share resources and memory, so communication is cheaper than between processes, and throughput rises on multicore machines.
In OOP it is used in GUI applications, web servers handling many clients, games, real-time simulation and concurrent data processing.
Shared data needs synchronization, using std::mutex, to avoid race conditions.
Types of collections are sequence (vector, list, deque), associative (set, map), unordered (unordered_set, unordered_map) and adaptors (stack, queue, priority_queue).
A collection class hides storage and offers insert, erase, search and iterate operations for any type through templates.

Example.

void hello(int n) { cout << "worker " << n << "\n"; }
int main() {
  thread t(hello, 1);   // start
  t.join();             // wait for it
  cout << "done";       // worker 1, then done
}

Comparison (Dec 2024).

Collection	Access	Insert/Delete	Use case
vector	O(1) index	O(1) at end, O(n) middle	Default dynamic array
list	O(n)	O(1) at known position	Frequent insertion, deletion
map	O(log n)	O(log n)	Sorted key-value data
unordered_map	O(1) average	O(1) average	Fast lookup by key
set	O(log n)	O(log n)	Unique sorted elements

Answer frame. Open with the definition of multithreading; draw the lifecycle; develop points 1-6, then the collection types and the collection class; for Dec 2024 give the table then a use case per container; close with one line that multithreading gives speed and collections give organised data.

Asked: [7 marks] (Dec 2023, Dec 2024) What is Multithreading? Discuss its importance and application in OOP. Describe multi-threading and its advantages. Asked: [7 marks] (Jun 2020, Jun 2023) Explain multithreading in OOP, its benefits. Discuss the collection and its type. What is a collection class? Asked: [7 marks] (Dec 2024) Discuss various data collections available in C++. How do they differ in performance and use cases? Asked: [7 marks] (Dec 2025) Discuss data collections with a suitable case study (ATM/Library). Asked: [14 marks] (Nov 2018) Short notes (any two): Data collections, Destruction, Overloading. Asked: [14 marks] (Dec 2020) Short notes (any two): Multi-threading, Association, Access modifier. Asked: [14 marks] (Nov 2022) Short notes (any two): Virtual function, File Handling, Data collection.

Case study: ATM, Library management system

Definition. <mark>A case study applies object-oriented methodology to a real system: identify objects and classes from the problem, give them attributes and operations, and join them by associations.</mark>

Diagram. <figure class="ds-fig" style="margin:1.4rem 0;overflow-x:auto"><svg xmlns="http://www.w3.org/2000/svg" id="dsfig-u5-02" viewBox="0 0 338 252" width="338" height="252" role="img" aria-label="Library classes: Librarian(L), Member(M), Book(B), Loan(Ln); Lb = Library holding all"><style>#dsfig-u5-02 .e{stroke:#454C5A;stroke-width:1.4;fill:none}#dsfig-u5-02 .e.hi{stroke:#2340B8;stroke-width:2.6}#dsfig-u5-02 .n{fill:#FFFFFF;stroke:#16181D;stroke-width:1.4}#dsfig-u5-02 .n.hi{fill:#E3E9FC;stroke:#2340B8;stroke-width:2.2}#dsfig-u5-02 .n.rb-b{fill:#16181D;stroke:#16181D}#dsfig-u5-02 .n.rb-r{fill:#BD3227;stroke:#BD3227}#dsfig-u5-02 text{font-family:"JetBrains Mono",ui-monospace,Menlo,Consolas,monospace;font-size:13px}#dsfig-u5-02 .t{fill:#16181D;font-weight:500}#dsfig-u5-02 .t.inv{fill:#FFFFFF;font-weight:700}#dsfig-u5-02 .kd{stroke:#16181D;stroke-width:1.2}#dsfig-u5-02 .dot{fill:#16181D}#dsfig-u5-02 .ann{fill:#2340B8;font-size:11px;font-weight:700}#dsfig-u5-02 .lbl{fill:#6F7787;font-family:system-ui,-apple-system,sans-serif;font-size:12px;font-weight:700}#dsfig-u5-02 .ptr{fill:#2340B8;font-size:12px;font-weight:700}#dsfig-u5-02 .ah{fill:#454C5A}#dsfig-u5-02 .ah.hi{fill:#2340B8}#dsfig-u5-02 .wl rect{fill:#FFFFFF;stroke:#DCE0E7}#dsfig-u5-02 .wl .t{font-size:12px;font-weight:700}#dsfig-u5-02 .wl.hi rect{fill:#2340B8;stroke:#2340B8}#dsfig-u5-02 .wl.hi .t{fill:#FFFFFF}html.dark #dsfig-u5-02 .e{stroke:#B1B7C3}html.dark #dsfig-u5-02 .e.hi{stroke:#8FA3FF}html.dark #dsfig-u5-02 .n{fill:#161920;stroke:#E6E8ED}html.dark #dsfig-u5-02 .n.hi{fill:#1E2748;stroke:#8FA3FF}html.dark #dsfig-u5-02 .n.rb-b{fill:#E6E8ED;stroke:#E6E8ED}html.dark #dsfig-u5-02 .n.rb-r{fill:#FF7E71;stroke:#FF7E71}html.dark #dsfig-u5-02 .t{fill:#E6E8ED}html.dark #dsfig-u5-02 .t.inv{fill:#0F1115}html.dark #dsfig-u5-02 .kd{stroke:#E6E8ED}html.dark #dsfig-u5-02 .dot{fill:#E6E8ED}html.dark #dsfig-u5-02 .ann{fill:#8FA3FF}html.dark #dsfig-u5-02 .lbl{fill:#858D9C}html.dark #dsfig-u5-02 .ptr{fill:#8FA3FF}html.dark #dsfig-u5-02 .ah{fill:#B1B7C3}html.dark #dsfig-u5-02 .ah.hi{fill:#8FA3FF}html.dark #dsfig-u5-02 .wl rect{fill:#161920;stroke:#2A2E37}html.dark #dsfig-u5-02 .wl.hi rect{fill:#8FA3FF;stroke:#8FA3FF}html.dark #dsfig-u5-02 .wl.hi .t{fill:#0F1115}</style><defs><marker id="ah12" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="ah" d="M0,1 L9,5 L0,9 z"/></marker><marker id="ahh12" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="ah hi" d="M0,1 L9,5 L0,9 z"/></marker></defs><path class="e" d="M59,40 L279,40"/><path class="e" d="M51.4,55.2 L157.6,196.8"/><path class="e" d="M298,59 L298,191" marker-end="url(#ah12)"/><path class="e" d="M279,212 L190,212" marker-end="url(#ah12)"/><path class="e" d="M40,193 L40,59"/><g class="wl"><rect x="138.3" y="31" width="61.5" height="18" rx="9"/><text class="t" x="169" y="40" dy=".35em" text-anchor="middle">manages</text></g><g class="wl"><rect x="70.2" y="117" width="68.7" height="18" rx="9"/><text class="t" x="104.5" y="126" dy=".35em" text-anchor="middle">catalogs</text></g><g class="wl"><rect x="267.3" y="117" width="61.5" height="18" rx="9"/><text class="t" x="298" y="126" dy=".35em" text-anchor="middle">borrows</text></g><g class="wl"><rect x="220.3" y="203" width="26.4" height="18" rx="9"/><text class="t" x="233.5" y="212" dy=".35em" text-anchor="middle">of</text></g><circle class="n" cx="40" cy="40" r="18"/><text class="t" x="40" y="40" dy=".35em" text-anchor="middle">L</text><circle class="n" cx="298" cy="40" r="18"/><text class="t" x="298" y="40" dy=".35em" text-anchor="middle">M</text><circle class="n" cx="169" cy="212" r="18"/><text class="t" x="169" y="212" dy=".35em" text-anchor="middle">B</text><circle class="n" cx="298" cy="212" r="18"/><text class="t" x="298" y="212" dy=".35em" text-anchor="middle">Ln</text><circle class="n" cx="40" cy="212" r="18"/><text class="t" x="40" y="212" dy=".35em" text-anchor="middle">Lb</text></svg><figcaption style="font-size:.82em;opacity:.72;margin-top:.45rem">Library classes: Librarian(L), Member(M), Book(B), Loan(Ln); Lb = Library holding all</figcaption></figure>

Key points.

Methodology steps are analysis (find nouns as classes: Book, Member, Librarian, Loan), design (attributes and methods), then implementation.
Book has ISBN, title, author and status, with methods issue() and returnBook().
Member has id, name and borrowed books, with borrow() and return().
Librarian adds books, registers members and issues them; Loan links Member to Book with issue date, due date and fine.
Associations: a Member borrows 0..* Books through Loans; a Library aggregates many Books and Members.
Issue works as: search catalog, check the member, check availability, create a Loan and mark the book unavailable; return computes the fine.
Strings hold titles, names and ISBN; exceptions handle book unavailable, invalid member ID and overdue limit; a map<string, Book> or vector holds the catalog and users.
An ATM follows the same pattern: Account, Card, Transaction and Bank classes, with an exception for insufficient balance.

Answer frame. Open with the entities; draw the class diagram with attributes, methods and multiplicities; explain issue and return workflow; for the architecture question add the UI, business logic and storage layers and the use of strings, exceptions and collections; close with one line on reuse and maintainability.

Asked: [7 marks] (Jun 2023, Dec 2024) Explain library management system using object-oriented diagram; architecture and functionalities, and use of strings, exception handling and collections. Asked: [7 marks] (Dec 2020) Explain library management system using object oriented diagram. Asked: [7 marks] (Jun 2020) Explain the object oriented methodology of designing a library management system; the object and class diagrams. Asked: [14 marks] (May 2019) Explain briefly: Containers, Destruction, ATM.

Last-minute revision

Exception = abnormal runtime condition; handled with try, throw, catch.
Unmatched exception calls terminate(); catch(...) catches all.
Standard exceptions: bad_alloc, out_of_range, invalid_argument, bad_cast.
Thread lifecycle: New, Runnable, Running, Blocked, Terminated.
Threads share heap and data, but each has its own stack.
Use thread t(f); t.join(); and std::mutex for shared data.
vector access O(1); list insertion O(1); map O(log n); unordered_map O(1) average.
C string ends with '\0'; std::string has length, append, substr, find, compare.
Destructor releases resources when an object is destroyed.
Library classes: Book, Member, Librarian, Loan; ATM: Account, Card, Transaction.

Memory hooks

TTC: Try, Throw, Catch.
Thread = light worker inside a process; process = the whole factory.
VLMU: vector, list, map, unordered_map.
Library: Books are lent to Members by Librarian through a Loan.

Coverage checklist

Strings: Nov 2022 string functions.
Exceptional handling: May 2019, Nov 2019, Dec 2020, Jun 2020, Jun 2023, Dec 2023, Nov 2022 and Dec 2025, Nov 2018.
Introduction of Multi-threading and Data collections: Nov 2018, Dec 2020, Nov 2022, Jun 2020, Jun 2023, Dec 2023, Dec 2024, Dec 2025.
Case study like: ATM, Library management system: Dec 2020, Jun 2020, Jun 2023, Dec 2024, May 2019.