Throwing exceptions in C++ - Step-by-Step Execution

Concept Flow - Throwing exceptions

Start

↓

Check condition

Yes↓

Throw exception

↓

Catch exception?

No→Program terminates

Yes↓

Handle exception

↓

Continue or exit

The program checks a condition, throws an exception if needed, then tries to catch and handle it before continuing or stopping.

Execution Sample

C++

#include <stdexcept>

int main() {
  int x = -1;
  if (x < 0) throw std::runtime_error("Negative value");
  return 0;
}

This code throws an exception if x is negative.

Execution Table

Step	Action	Condition	Result	Exception Thrown	Program Flow
1	Initialize x	N/A	x = -1	No	Continue
2	Check if x < 0	x < 0	True	Yes	Throw exception
3	Exception thrown	N/A	runtime_error("Negative value")	Yes	Program looks for catch block
4	No catch block found	N/A	N/A	Yes	Program terminates with error

💡 Program stops because exception was thrown and not caught

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	undefined	-1	-1	-1

Key Moments - 2 Insights

Why does the program stop after throwing the exception?

Because there is no catch block to handle the exception, as shown in step 4 of the execution table, the program terminates.

Is the exception thrown before or after checking the condition?

The exception is thrown only after the condition (x < 0) is checked and found true, as shown in step 2 and 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of x at step 2?

A undefined

B 0

C -1

D 1

💡 Hint

Check the 'Condition' and 'Result' columns at step 2 in the execution table.

At which step does the program throw the exception?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look for the 'Exception Thrown' column in the execution table.

If a catch block was added, what would happen at step 4?

A Exception is handled and program continues

B Exception is ignored

C Program terminates with error

D Program restarts

💡 Hint

Refer to the 'Program Flow' column and think about exception handling.

Concept Snapshot

Throwing exceptions in C++:
- Use 'throw' keyword to signal an error.
- Exception interrupts normal flow.
- Must be caught by 'try-catch' blocks to handle.
- If uncaught, program terminates.
- Example: if (x < 0) throw std::runtime_error("error");

Full Transcript

This example shows how throwing exceptions works in C++. The program starts by setting x to -1. It checks if x is less than zero. Since it is, the program throws a runtime_error exception. Because there is no catch block to handle this exception, the program stops immediately with an error. Throwing exceptions interrupts normal program flow and requires handling with try-catch blocks to avoid termination.