Final answer:
An assertion before a statement states the logical conditions that must hold true, an assertion after a statement states the expected result, and a weakest precondition guarantees the desired outcome.
Step-by-step explanation:
An assertion before a statement states the logical conditions that must hold true in order for the statement to be executed. For example, if you want to divide a number by 2, you can include an assertion before the statement to check if the number is even. If the assertion is false, the statement can be skipped or an error can be raised. An assertion following a statement states the expected result or condition that should hold true after the statement has been executed. For example, if you write a program to add two numbers, you can include an assertion after the addition statement to check if the sum is equal to the expected result.
A weakest precondition is the least restrictive condition that must hold true before the execution of a statement to guarantee the desired outcome. It represents the minimum requirements or assumptions necessary for the statement to be executed correctly. For example, if you have a statement that expects a positive number as input, the weakest precondition could be that the number is greater than 0.