Chapter8 - Programming

Programming concepts

Variables and constants

Python：

# variable
firstVar = 20

# constant
FIRST_CONSTANT = 20

Pseudocode

DECLARE FirstVar: Integer
FirstVar = 10

CONSTANT FirstConst = 500

Basic Data Types

pseudocode
  • Integer – a positive or negative whole number that can be used with mathematical operators.
  • Real – a positive or negative number with a fractional part; real numbers can be used with mathematical operators.
  • Char – a variable or constant that is a single character.
  • String – a variable or constant that is several characters in length.
  • Boolean – a variable or constant that can have only two values, TRUE or FALSE.

pseudocode

DECLARE FirstInt : INTEGER 
DECLARE FirstReal : REAL 
DECLARE Female : CHAR 
DECLARE FirstName : STRING 
DECLARE Flage : BOOLEAN
python::

Python

firstInt = 25 
firstReal = 25.0 
female = 'F' 
firstName = 'Emma' 
flag = True

Input and Output

pseudocode

INPUT FirstInt

OUTPUT "Enter a whole number "

OUTPUT "Number is " FirstInt

python

a = input()

b = input("Enter a whole number")

c = int(b)

firstInt = int(input ("Enter a whole number"))

print("number is: ", firstInt)

Basic concepts

Sequence

The ordering of the steps in an algorithm.

An incorrect order can lead to incorrect results or unnecessary extra steps.

Selection

This allows different routes through the steps of a program.

pseudocode

IF Age > 17 
  THEN 
    OUTPUT "You are an adult" 
  ELSE 
    OUTPUT "You are a child" 
ENDIF

CASE OF OpValue 
  "+" : Answer = Number1 + Number2 
  "-" : Answer = Number1 - Number2 
  "*" : Answer = Number1 * Number2 
  "/" : Answer = Number1 / Number2 
  OTHERWISE OUTPUT "invalid operator"
ENDCASE

python

if Age > 17:
    print("You are an adult")
else:
    print("You are a child")
    
# Python doesn't have switch case
    
if opValue == "+":
    answer = number1 + number2 
elif opValue == "-":
    answer = number1 - number2 
elif opValue == "*":
    answer = number1 * number2 
elif opValue == "/":
    answer = number1 / number2 
else: 
    print("invalid operator")
iteration
  1. count-controlled loops (for a set number of iterations)
  2. pre-condition loops – may have no iterations
  3. post-condition loops – always has at least one iteration.

pseudocode

FOR Counter ← 1 TO 10 STEP 2 
    OUTPUT Counter 
NEXT Counter


WHILE TotalWeight < 100 
    TotalWeight = TotalWeight + Weight 
ENDWHILE

REPEAT 
    NumberOfItems = NumberOfItems + 1 
UNTIL NumberOfItems > 19

python

for Counter in range (1,10,2):
    print(Counter)
    
while TotalWeight < 100:
    TotalWeight = TotalWeight + Weight
Totalling and counting

pesudocode

# Totalling
TotalWeight = TotalWeight + Weight

# Counting
NumberOfItems = NumberOfItems + 1
String handling

Strings store text:: every string contains several characters and each character in a string can be found by its position number.

The first character of a string in pseudocode is at position 1; the first character of a string is at position zero for Java, Python and Visual Basic.

  1. Length – finding the number of characters in the string. For example, the length of the string "Computer Science" is 16 characters as spaces are counted as a character.
  2. Substring – extracting part of a string. For example, the substring "Science" could be extracted from "Computer Science". First parameter is the string, second parameter is the position of the start character, third parameter is the length of the required substring.
  3. Upper – converting all the letters in a string to uppercase. For example, the string "Computer Science" would become "COMPUTER SCIENCE".
  4. Lower – converting all the letters in a string to lowercase. For example, the string "Computer Science" would become "computer science".

pseudocode

LENGTH("Computer Science") 
LENGTH(MyString)

SUBSTRING("Computer Science", 10, 7) 
SUBSTRING(MyString, 10, 7)

UCASE("Computer Science") 
UCASE(MyString)

LCASE("Computer Science") 
LCASE(MyString)
Arithmetic, logical and Boolean operators
  1. arithmetic operators – for calculations (+, -, *, /, ^, MOD, DIV)
  2. logical – for comparisons
  3. Boolean – to decide whether an expression is true or false.

Use of nested statements

Selection and iteration statements can be nested one inside another.

Procedures and functions

  1. A procedure is a set of programming statements grouped together under a single name that can be called to perform a task at any point in a program.
  2. A function is a set of programming statements grouped together under a single name that can be called to perform a task at any point in a program. A function returns a value back to the main program.
  3. Parameters are the variables that store the values of the arguments passed to a procedure or function. Some procedures and functions will have parameters.

pseudocode

PROCEDURE Stars 
    OUTPUT "********" 
ENDPROCEDURE


PROCEDURE Stars (Number:INTEGER) 
    DECLARE Counter : INTEGER 
    FOR Counter ← 1 TO Number 
        OUTPUT "*" 
    NEXT 
ENDPROCEDURE

FUNCTION Celsius(Temperature: REAL) RETURNS REAL 
    RETURN (Temperature – 32) / 1.8 
ENDFUNCTION

Python

def Stars():
    print("************")
    
def Stars(Number):
    for counter in range (Number):
        print("*", end = '')

def Celsius(Temperature):
    return (Temperature - 32) / 1.8

Local and global variables

A global variable can be used in any part of a program – its scope covers the whole program.

A local variable can only be used by the part of the program it has been declared in; it is restricted to that part of the program.

Library routines

Library routines are fully tested and ready for use in a program.

  1. MOD – returns remainder of a division
  2. DIV – returns the quotient (that is, the whole number part) of a division
  3. ROUND – returns a value rounded to a given number of decimal places
  4. RANDOM – returns a random number.

pseudocode

Value1 ← MOD(10, 3) 
Value2 ← DIV(10, 3) 
Value3 ← ROUND(6.97354, 2) 
Value4 ← RANDOM()

python

value1 = 10%3 
value2 = 10//3 
value = divmod(10,3) 
value3 = round(6.97354, 2) 


from random import random 
value4 = random()

Creating a maintainable program

  1. always use meaningful identifier names for variables, constants, arrays, procedures and functions
  2. be divided into modules for each task using procedures and functions
  3. be fully commented using your programming language’s commenting feature.

pseudocode

// pseudocode uses a double slash to start a comment

python


#Python uses hash to start a comment for every line

8.02 Arrays

One- and tow- dimensional arrays

Declaring and populating arrays with iteration

pesudocode

DECLARE MyTable : ARRAY[0:9,0:2] OF INTEGER 

OUTPUT “Enter these values in order” 
OUTPUT “27, 19, 36, 42, 16, 89, 21, 16, 55, 34” 
OUTPUT “31, 67, 98, 22, 35, 46, 71, 23, 11, 76” 
OUTPUT “17, 48, 29, 95, 61, 47, 28, 13, 77, 21” 
FOR ColumnIndex ← 0 TO 2
    FOR RowIndex ← 0 TO 9
        OUTPUT “Enter next value “
        INPUT MyTable[RowIndex, ColumnIndex]
    NEXT RowIndex 
NEXT ColumnIndex

8.03 File handling

Purpose of storing data in a file

Computer programs store data that will be required again in a file.

Using files

pseudocode

DECLARE TextLine : STRING 
DECLARE MyFile : STRING


MyFile ← "MyText.txt"
// variables are declared as normal

// writing the line of text to the file 
OPEN MyFile FOR WRITE  // opens file for writing
    OUTPUT "Please enter a line of text"
    INPUT TextLine
    WRITEFILE, TextLine // writes a line of text to the file 
CLOSEFILE(MyFile) // closes the file

// reading the line of text from the file 
OUTPUT "The file contains this line of text:" 
OPEN MyFile FOR READ // opens file for reading
    READFILE, TextLine // reads a line of text from the file
    OUTPUT TextLine 
CLOSEFILE(MyFile) // closes the file