The Elegance of Addition

Addition is straightforward, isn't it? When we encounter a number in our expression string, we simply add it to our running total, which we'll call result. That's about it for addition.

Subtraction as "Negative Addition"

Here's where the subtlety comes in. Instead of thinking of subtraction as a separate operation, let's reframe it as adding a negative number. This concept simplifies our logic beautifully. Now, we don't have to juggle between two different operations; it's all addition!

A Practical Example: '1-1'

To illustrate how this works, let's consider the expression 1-1. Our logic could flow as follows:

1. Initialize result to 0.
2. Loop through each character in the string '1-1'.
3. Identify what each character is:

• If it's a number, add it to result.
• If it's a - sign, prepare to make the next number negative.

By following these steps, we'll add 1 to result, and then effectively add -1 to result, resulting in a final value of 0.