C++ Streams, Formatted I/O & Exception Handling

1. What is a Stream in C++? (In Simple Words)

Think of a Stream like water flowing through a pipe.

In C++, input and output are treated as a continuous flow (stream) of bytes moving between your program and devices:

• Input Stream: Bytes flowing from an input device (like keyboard or file) into the program (cin >>).
• Output Stream: Bytes flowing from your program out to a destination (like monitor screen or printer) (cout <<).

                     ┌──────────────────┐
[ Keyboard / File ] ─┤   INPUT STREAM   ├──▶ [ C++ Program in RAM ]
                     └──────────────────┘               │
                                                        ▼
                     ┌──────────────────┐      ┌─────────────────┐
[ Monitor Screen ]  ◀┤  OUTPUT STREAM   ├──────┤   cout << text  │
                     └──────────────────┘      └─────────────────┘

2. C++ Stream Class Hierarchy

C++ organizes all input and output classes into a neat family tree:

3. Unformatted vs. Formatted I/O Operations

A. Unformatted I/O (Raw Character Data)

Reads and writes raw characters without any special formatting or columns:

B. Formatted I/O Using <iomanip> Manipulators

Manipulators change how output is displayed (adding columns, padding characters, or setting decimal places):

#include <iostream>
#include <iomanip> // Must include for setw, setprecision!
using namespace std;

int main() {
    cout << "=== Formatted Account Statement ===" << endl;

    // setw(w): sets column width
    // setfill(ch): fills empty spaces with a custom character
    // fixed + setprecision(n): sets exact decimal places
    cout << left << setw(15) << setfill('.') << "Customer" 
         << right << setw(15) << setfill(' ') << "Balance (INR)" << endl;

    cout << left << setw(15) << setfill('.') << "Rohit Sharma" 
         << right << setw(15) << setfill(' ') << fixed << setprecision(2) << 14500.75 << endl;

    cout << left << setw(15) << setfill('.') << "Priya Joshi" 
         << right << setw(15) << setfill(' ') << fixed << setprecision(2) << 890.00 << endl;

    return 0;
}

4. Exception Handling in C++ (try, catch, throw)

In simple programs, we use if-else to check errors. But for serious errors (like dividing by zero, missing file, or running out of RAM), using too many if-else statements makes code messy.

Exception Handling is a clean way to detect and handle runtime errors so the program does not crash suddenly.

5. Practical Code Example: Safe Division Calculator

Dividing by zero in math is undefined. In C++, normal division by zero crashes your program! Here is how we handle it gracefully:

#include <iostream>
using namespace std;

float divide(float a, float b) {
    if (b == 0.0f) {
        // THROW an error message when denominator is zero!
        throw "Error: Division by zero is mathematically impossible!";
    }
    return a / b;
}

int main() {
    float num, den;
    cout << "Enter Numerator and Denominator: ";
    cin >> num >> den;

    // 1. TRY: Run the calculation safely
    try {
        float ans = divide(num, den);
        cout << "Result: " << ans << endl;
    }
    // 2. CATCH: Catch the specific string error message
    catch (const char *msg) {
        cout << "\n[EXCEPTION CAUGHT] " << msg << endl;
        cout << "Please re-run the program with a non-zero denominator." << endl;
    }
    // 3. CATCH-ALL: Fallback for any unknown errors
    catch (...) {
        cout << "[UNKNOWN ERROR] An unexpected error occurred!" << endl;
    }

    cout << "\nProgram continues running normally..." << endl;
    return 0;
}

DAVV Exam Preparation Tips

Frequently Asked 5-Mark Questions:

1. Explain the C++ Stream Class Hierarchy.
   Model Answer:
   • Draw the diagram with ios as the base class.
   • Show istream (for cin) and ostream (for cout) inheriting from ios.
   • Show iostream inheriting from both istream and ostream (Multiple Inheritance).
2. Explain the keywords try, catch, and throw in C++.
   Model Answer:
   • try: Marks a block of code to be monitored for errors.
   • throw: Throws an exception when an error occurs.
   • catch: Catches and handles the exception.

Frequently Asked 10-Mark Questions:

1. Explain Formatted and Unformatted I/O in C++. Detail at least four manipulators from <iomanip> with code examples. Discuss Exception Handling with multiple catch blocks and the catch-all (catch(...)) handler.
   Model Answer:
   • Explain unformatted functions: get(), put(), getline(), and write().
   • Explain manipulators: setw(), setprecision(), setfill(), and endl.
   • Explain the concept of Exception Handling and why it is better than nested if-else.
   • Write out the complete C++ program for division by zero with try, catch(const char*), and catch(...).