Difficulty: Medium

Average Score: 70%

The steps in an algorithm to calculate the positive difference in two given values, z and y, are given in no particular order.
Put Diff to output.
Set Diff x-y.
If y>, set Diff = y - 2.
Declare variable Diff.

What is the first step of the algorithm?

Rationale

Declare variable Diff.

The first step in an algorithm is to declare any variables that will be used, which sets the stage for the operations that follow. In this case, declaring the variable 'Diff' is essential to ensure that it can be utilized for storing the computed difference later in the algorithm.

A (Set Diff = x - y.) YOUR ANSWER

This step indicates an operation that occurs after the variable has been declared. Setting 'Diff' to the value of 'x - y' requires that 'Diff' already exists, making this step invalid as the first action in the algorithm.

B (If y > x, set Diff = y - x.) YOUR ANSWER

This conditional statement is dependent on the variable 'Diff' being declared first. Since it involves a comparison and a potential assignment, it cannot be executed until after the variable has been initialized, making it unsuitable as the initial step.

C (Declare variable Diff.) CORRECT

This is the correct answer as it establishes 'Diff' as a variable that can later hold the positive difference between 'z' and 'y'. Declaring the variable first is crucial for the algorithm to function correctly, allowing subsequent steps to utilize 'Diff'.

D (Put Diff to output.) YOUR ANSWER

Outputting 'Diff' is a final step that relies on the variable having been calculated and assigned a value. As such, it cannot be the first step, since it presupposes that all previous calculations and assignments have already taken place.

Conclusion

In an algorithm, the initial step is to declare any necessary variables, which allows for their use in subsequent calculations and operations. In this case, declaring 'Diff' is essential for the algorithm's function, as it must exist before any computations or outputs can be performed. All other options are dependent on this foundational step and cannot be executed until after 'Diff' has been declared.

What is the first step of the algorithm?

Declare variable Diff.

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