Welcome to this thrilling session on runtime errors in C++ programming. We're going to delve into runtime errors, understand their types and occurrences, and learn how to handle them. Mastering this will make your C++ code reliable and fail-safe.

Today, we'll dissect runtime errors, categorize them, and learn how to identify and prevent them in C++ programs.

Runtime errors appear during your program's execution and prevent the program from running as expected. Such errors occur when commands, even though syntactically correct, are logically impossible to execute.

Runtime errors occur in various forms, including:

1. Null pointer dereferences: Attempting to access a null pointer’s property.
2. Division by zero: Attempting to divide a number by zero.
3. Accessing uninitialized variables: Using a variable that has not been assigned a value.

Below are examples for each type

C++
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1#include <iostream>
2
3int main() {
4    int* ptr = nullptr;
5    std::cout << *ptr << std::endl;  // Null pointer dereference error.
6    return 0;
7}

In this example, ptr is assigned the value nullptr. Attempting to dereference the null pointer with *ptr results in a runtime error since the pointer does not point to a valid memory address.

C++
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1#include <iostream>
2
3int main() {
4    int number = 1;
5    int zero = 0;
6    std::cout << number / zero << std::endl;  // Division by zero error.
7    return 0;
8}

Here, number is divided by zero. Division by zero is mathematically undefined and causes a runtime error in the program.

C++
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1#include <iostream>
2
3int main() {
4    int uninitVar;  // Variable declared but not initialized.
5    std::cout << uninitVar << std::endl;  // Undefined behavior: accessing uninitialized variable.
6    return 0;
7}

This example declares uninitVar but does not initialize it. Accessing the uninitialized variable through cout leads to undefined behavior and potential runtime errors since its value is indeterminate.

Programmatically preventing error conditions can help fix runtime errors:

C++
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1#include <iostream>
2
3int main() {
4    int number = 10;
5    int zero = 0;
6    if (zero != 0) {
7        std::cout << number / zero << std::endl;
8    } else {
9        std::cout << "Cannot divide by zero." << std::endl;
10    }
11    return 0;
12}

This code snippet introduces basic error handling by implementing an if-else condition. It first checks if the divisor is not zero before executing a division operation that could potentially result in a runtime error. This simple yet effective method prevents the common runtime error of dividing by zero. The division proceeds if the condition is met (the divisor is not zero); otherwise, a message is printed to inform that division by zero is impossible, thereby avoiding the error and making the program more robust.

We've completed our lesson on runtime errors in C++, their types, identification, and prevention measures.

With well-crafted practice exercises arriving shortly, you'll get the chance to apply your newly acquired understanding. So stay tuned, and happy learning!