Unit 4 #5

Consider the following procedures, which are used to control a device that draws lines on paper.

Consider the goal of using the device to produce the following drawing, where each line shown has a length of 10 units and the horizontal lines are 10 units apart.

The device is positioned at the upper-left corner of a sheet of paper and is facing right. Which of the following code segments will produce the drawing shown?

• penDown()

  goForward(10)

  turnRight(90)

  goForward(10)

  turnRight(90)

  goForward(10)

• penDown()

  goForward(10)

  penUp()

  turnRight(90)

  turnRight(90)

  penDown()

  goForward(10)

• penDown()

  goForward(10)

  turnRight(90)

  penUp()

  goForward(10)

  turnRight(90)

  penDown()

• penDown()

  goForward(10)

  penUp()

  turnRight(90)

  goForward(10)

  turnRight(90)

  penDown()

  goForward(10)

Which of the following are ways in which a programmer can use abstraction to manage the complexity of a program?

Select two answers.

response - correct

Responses

• Replacing each instance of repeated code with a call to a procedure

• Replacing longer variable names with shorter variable names to reduce typing errors

• 
  Replacing several lines of documentation with a single line of documentation

• Replacing several lines of documentation with a single line of documentation name1,  name2, name3, and name4 with a list of strings
  called names

Which of the following are benefits of procedural abstraction?

Select two answers.

• Procedural abstraction prevents programmers from accidentally using the intellectual property of other programmers.

• Procedural abstraction eliminates the need for programmers to document their code.

• Procedural abstraction makes it easier for people to read computer programs.

• Procedural abstraction provides an opportunity to give a name to a block of code that describes the purpose of the code block.

Consider the following procedure.

PROCEDURE doSomething(num1, num2)

{

DISPLAY(num1)

RETURN(num1)

DISPLAY(num2)

}

Consider the following statement.

DISPLAY(doSomething(10, 20))

What is displayed as a result of executing the statement above?

Responses

• 10 10

• 10 20

• 10 10 20

• 10 20 10

Consider the following procedure.

Procedure CallExplanationdrawLine(x1, y1, x2, y2)Draws a line segment on a coordinate grid with endpoints at coordinates (x1, y1) and (x2, y2)

The drawLine procedure is to be used to draw the following figure on a coordinate grid.

Which of the following code segments can be used to draw the figure?

Responses

• xVal ← 1

  yVal ← 0

  len ← 1

  REPEAT 5 TIMES

  {

  drawLine(xVal, yVal, xVal, yVal + len)

  xVal ← xVal + 1

  len ← len + 1

  }

• xVal ← 1

  yVal ← 0

  len ← 1

  REPEAT 5 TIMES

  {

  drawLine(xVal, yVal, xVal + len, yVal)

  yVal ← yVal + 1

  len ← len + 1

  }

• xVal ← 5

  yVal ← 0

  len ← 5

  REPEAT 5 TIMES

  {

  drawLine(xVal, yVal, xVal, yVal + len)

  xVal ← xVal - 1

  }

• xVal ← 5

  yVal ← 0

  len ← 5

  REPEAT 5 TIMES

  {

  drawLine(xVal, yVal, xVal + len, yVal)

  yVal ← yVal - 1

  len ← len - 1

  }

The following question uses a robot in a grid of squares. The robot is represented by a triangle, which is initially facing right.

Consider the following procedure.

Which of the following code segments will move the robot to the gray square along the path indicated by the arrows?

• 
• 
• 
• 

A student is developing a program that allows users to look up the definitions of words that appear in a book.

The student plans to perform a large number of searches through a dictionary containing words and their definitions. The student will use a procedure written by a computer scientist to quickly search the dictionary (and knows that the procedure will return a definition if one is available). The student cannot modify the search procedure written by the computer scientist but can call the procedure by supplying a word.

Which of the following is a true statement about the student’s use of the computer scientist’s search procedure?

• The student is changing the search procedure’s internal abstractions.

• The student is modifying the search procedure to take a definition as an argument and return the corresponding word.

• The student is reusing the computer scientist’s procedural abstraction by knowing what the procedure does without knowing how it does it.

• The student is reusing the computer scientist’s procedural abstraction by using duplicate code each time a search needs to occur.

Consider the following procedure.

Procedure CallExplanationdrawCircle(xPos, yPos, rad)Draws a circle on a coordinate grid with center (xPos, yPos) and radius rad

The drawCircle procedure is to be used to draw the following figure on a coordinate grid.

Which of the following code segments can be used to draw the figure?

Select two answers.

• x ← 4

  y ← 1

  r ← 0

  REPEAT 3 TIMES

  {

  drawCircle(x, y, r)

  r ← r + 1

  y ← y + 1

  }

• x ← 4

  y ← 1

  r ← 0

  REPEAT 3 TIMES

  {

  r ← r + 1

  y ← y + 1

  drawCircle(x, y, r)

  }

• x ← 4

  y ← 4

  r ← 3

  REPEAT 3 TIMES

  {

  drawCircle(x, y, r)

  y ← y - 1

  r ← r - 1

  }

• x ← 4

  y ← 4

  r ← 3

  REPEAT 3 TIMES

  {

  y ← y - 1

  r ← r - 1

  drawCircle(x, y, r)

  }

The procedure  can be used to draw a circle on a coordinate grid. The circle is centered at the coordinate  and has a radius of units. The procedure will be used to draw the following figure on a coordinate grid.

Which of the following code segments can be used to draw the figure?

• 
• 
• 
• 

A computer science student completes a program and asks a classmate for feedback. The classmate suggests rewriting some of the code to include more procedural abstraction. Which of the following is NOT a benefit of procedural abstraction?

Responses

• Making the code more readable

• Making the code run faster

• Providing more opportunities for code reuse

• Reducing the amount of duplicated code