4.17. Pseudocode and Flowcharts

4.17.1. Pseudocode

When representing a function in pseudocode we use the keywords BEGIN and END to indicate the start and end of the function.

BEGIN function_name
    process
END function_name

If the function returns a value we use the keyword RETURN followed by the values that are returned

RETURN values

Here’s an example.

Python code

def add(x, y):
    return x + y

Pseudocode

BEGIN add (x, y)
    RETURN x + y
END add (x, y)

Once you have the pseudocode for a function, you can use this function in other scripts. For your main script you can simply use BEGIN and END.

Python code

def add(x, y):
    return x + y


for i in range(3):
    doubled = add(i, i)
    print(doubled)

Pseudocode

BEGIN
    FOR i = 0 TO 2 STEP 1
        doubled = add(i. i)
        Display doubled
END


BEGIN add (x, y)
    RETURN x + y
END add (x, y)

4.17.2. Flowcharts

We now introduce two new shapes. The terminator and the subprocess.

• Terminator - oval: Used to indicate the start and end of a program.

• Subprocess - bordered rectangle: Used to refer to another program

Here’s an example.

Python code

def add(x, y):
    return x + y


for i in range(3):
    doubled = add(i, i)
    print(doubled)

Flow chart

Note that there are two flow charts here. The first shows the main script and the second shows the function add(). The main script refers to the add() function in the subprocess node.

We have now seen all the flowchart symbols we will need.

Note that the colours are arbitrary and what’s important are the shapes.

Question 1

Which of the following programs corresponds to the pseudocode shown below?

BEGIN
    my_numbers = [5, -2, 0, 4, 0, -3, -3]
    description = []
    FOR i = 0 TO Length(my_numbers) - 1 STEP 1
        d = sign(my_numbers[i])
        Append d to description
    NEXT i
    Display description
END

BEGIN sign(x)
    IF x < 0 THEN
        RETURN 'negative'
    ELIF x > 0 THEN
        RETURN 'positive'
    ELSE
        RETURN '0'
END sign(x)

1. def my_numbers(5, -2, 0, 4, 0, -3, -3):
       description = []
       for i in range(len(my_numbers)):
           description.append(my_numbers[i])
       return description
   
   sign(x)
   if x < 0:
       return 'negative'
   elif x > 0:
       return 'positive'
   else:
       return '0'
   

2. def my_numbers(5, -2, 0, 4, 0, -3, -3):
       description = []
       for i in range(len(my_numbers)):
           description.append(my_numbers[i])
       return description
   
   def sign(x):
       if x < 0:
           return 'negative'
       elif x > 0:
           return 'positive'
       else:
           return '0'
   

3. def sign(x):
       if x < 0:
           print('negative')
       elif x > 0:
           print('positive')
       else:
           print('0')
   
   my_numbers = [5, -2, 0, 4, 0, -3, -3]
   description = []
   for i in range(len(my_numbers)):
       description.append(sign(my_numbers[i]))
   print(description)
   

4. def sign(x):
       if x < 0:
           return 'negative'
       elif x > 0:
           return 'positive'
       else:
           return '0'
   
   my_numbers = [5, -2, 0, 4, 0, -3, -3]
   description = []
   for i in range(len(my_numbers)):
       description.append(sign(my_numbers[i]))
   print(description)
   

Solution

1. Incorrect. In the pseudocode there is a function called sign(x). You can tell from the pseudocode because there is a BEGIN sign(x) and an END sign(x). There is no sign(x) function in the python code.

2. Incorrect. In the pseudocode there is no function my_numbers(5, -2, 0, 4, 0, -3, -3). This is a variable created in the main script. You can identify the main script because it has a BEGIN and END without a function name. this python code has a function called`` my_numbers``.

3. Incorrect. sign() should contain return statements, not print statements. The pseudocode has return statements.

4. Correct.

Question 2

Which of the following flowcharts corresponds to the pseudocode shown below?

BEGIN
    my_numbers = [5, -2, 0, 4, 0, -3, -3]
    description = []
    FOR i = 0 TO Length(my_numbers) - 1 STEP 1
        d = sign(my_numbers[i])
        Append d to description
    NEXT i
    Display description
END

BEGIN sign(x)
    IF x < 0 THEN
        RETURN 'negative'
    ELIF x > 0 THEN
        RETURN 'positive'
    ELSE
        RETURN '0'
END sign(x)

Solution

Solution is locked

Question 3

Construct the pseudocode that corresponds to the following Python function.

def zero_nonzero(number_list):
    zero = 0
    nonzero = 0
    for i in range(len(number_list)):
        if number_list[i] == 0:
            zero = zero + 1
        else:
            nonzero = nonzero + 1
    return zero, nonzero

Solution

Solution is locked

Question 4

Write the Python code the corresponds to the given flowchart.

Solution

Solution is locked