String Parsing and Arithmetic with C++

Welcome! Today, we have an intriguing and practical task at hand that will test your C++ programming skills. We will be maneuvering around parsing strings and making type conversions. So, let's launch into it!

Our task for the day involves creating a C++ function called ParseAndMultiplyNumbers(). This function is designed to accept a string as an input. However, it's not just any string — the input we're considering is a playful mix of numbers and words.

The purpose of this function is to analyze the input string, extract all the numbers, convert these numbers (currently string types) into integer data types, and then multiply all these numbers together. The final output? It's the product of all those numbers!

Here's an illustration for clarification. Given the input string "I have 2 apples and 5 oranges," our function should return the product of 2 and 5, which is 10.

The primary task is to parse the string and identify the numbers. To do that, let's create an empty string num to accumulate digits and a vector numbers to collect all the numbers we find:

std::string inputString = "I have 2 apples and 5 oranges";
std::string num;
std::vector<int> numbers;

The next step requires iterating through the input string character by character. When we encounter a digit, we append it to our num string. If a character isn’t a digit and num isn’t empty, it means we've reached the end of a number.

At this point, we convert num to an integer, add it to the numbers vector, and reset num to an empty string. If the character isn’t a digit and num is empty, we simply skip and progress.

for (char ch: inputString) {
    if (isdigit(ch)) {
        num += ch;
    } else if (!num.empty()) {
        numbers.push_back(stoi(num));
        num = "";
    }
}
for (int number: numbers) {
    std::cout << number << " ";
}

After running this code, the output should be "2 5".