Compilers use ASTs to optimize code.

The several stages of the compiler are responsible for diverse duties. For each activity, please provide specific instructions.

Explain how the compiler works and why it may be tested.

Barcode Validation As you are aware, barcodes encode numbers. In the Universal Product Code system, each item is assigned a globally unique number. But not every number is a valid UPC. Why? Part of the answer is the check digit. In order to catch errors, the rightmost digit is calculated from the others. If this digit does not match its expected value, you can be assured the barcode is invalid, or has been read incorrectly. To calculate the check digit, perform the following operations modulo 10: • Sum the digits in the odd positions and multiply the result by three. • Add the digits in the even positions to the result. • Subtract the result from 10 to obtain the check digit. Your Task Given a 12-digit UPC, you will need to identify whether is is valid or invalid. The code will be provided from standard input. You simply need to print "valid" or "invalid" in response. Notes The code will be provided on a line by itself, and will consist of numerals alone. You may assume that it will be...

Explain the compiler's structure and how the code may be tested.

Various design methods are used to increase readability of the code.

Incompatibility between Interpreters and Compilers

In the context of computer programming, what does it mean to "resist the urge to code"?