Introducing Calc

To make the following explanations, we will first define a toy programming language that we will name Calc (from the calculator). A toy programming language is a programming language used to demonstrate or prove something, not designed to develop real-world software. A simple program written in Calc is shown as follows:

@first
@second
> first
> second
@sum
sum := first + second
< sum
< first * second

The preceding program asks the user to type two numbers and then prints the sum and the product of those numbers on the console. Let's examine one statement at a time, as follows:

• The first two statements (@first and @second) declare two variables. Any variable in Calc represents a 64-bit floating-point number.
• The third and fourth statements (> first and > second) are input statements. Each of these prints a question mark and waits for the user to type a number and press Enter. Such a number, if valid, is stored in the specified variable. If no number or...