Try–catch block in C++ - Step-by-Step Execution

Concept Flow - Try–catch block

Start

↓

Try block begins

↓

Code runs

↓

Exception thrown?

No→Try block ends normally

|Yes↓

Catch block matches exception

↓

Catch block runs

↓

Continue after catch

↓

End

The program tries code inside the try block. If an error (exception) happens, it jumps to the matching catch block to handle it, then continues.

Execution Sample

C++

try {
  int x;
  int denom = 0;
  if (denom == 0) {
    throw std::runtime_error("Division by zero");
  }
  x = 10 / denom;
  std::cout << "No error" << std::endl;
} catch (const std::exception& e) {
  std::cout << "Error caught" << std::endl;
}

This code checks for division by zero before dividing, which causes an exception caught by the catch block that prints an error message.

Execution Table

Step	Action	Evaluation	Result
1	Enter try block	Start executing code inside try	Proceed
2	Check for division by zero	Division by zero detected	Exception thrown
3	Jump to catch block	Catch block matches std::exception	Catch block runs
4	Execute catch block	Print "Error caught"	Output: Error caught
5	Exit try-catch	Continue normal flow	Program continues

💡 Exception thrown at division by zero, caught by catch block, program continues after handling

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
x	undefined	Exception thrown, no value assigned	No change	No value assigned

Key Moments - 2 Insights

Why does the program jump to the catch block instead of crashing?

Because an exception was thrown inside the try block (see Step 2 in execution_table), the program looks for a matching catch block to handle it (Step 3), preventing a crash.

Does the code after the error inside the try block run?

No, once the exception is thrown (Step 2), the rest of the try block is skipped and control moves to the catch block (Step 3).

Visual Quiz - 3 Questions

Look at the execution table, what happens at Step 2?

A The catch block starts running

B The division by zero causes an exception to be thrown

C The program prints "No error"

D The try block finishes normally

💡 Hint

Check the 'Evaluation' and 'Result' columns at Step 2 in the execution_table

At which step does the catch block execute?

A Step 1

B Step 2

C Step 3

D Step 5

💡 Hint

Look for 'Jump to catch block' and 'Catch block runs' in the execution_table

If no exception was thrown, what would happen to the output?

A It would print "No error"

B It would print "Error caught"

C It would print nothing

D The program would crash

💡 Hint

Think about what happens if the try block finishes without exceptions (see Step 2 and exit_note)

Concept Snapshot

try {
  // code that might throw
} catch (ExceptionType e) {
  // handle error
}

- Code in try runs normally
- If error occurs, jump to matching catch
- Catch handles error, program continues
- Prevents crashes by managing exceptions

Full Transcript

A try-catch block lets your program try some code that might cause an error. If an error happens, the program jumps to the catch block to handle it safely. This way, the program does not crash but continues running after dealing with the problem. In the example, a division by zero check throws an exception caught by the catch block, which prints an error message. The code after the error inside try does not run. The catch block runs only if an exception occurs.