Back

Paper 2: Pseudocode | O Level Computer Science 2210 & IGCSE Computer Science 0478 | Detailed Free Notes To Score An A Star (A*)

Views 1
  • Basically pseudocode is not a programming language in the true sense.
  • Instead, it allows you to present a complex program that you have in your mind and want to build in the future in a non-language intensive and pure logic form.
  • As such, anyone can later understand that program in exactly what it has to do
  • Some of the common functions in pseudocode are as follows:
    • Variable
      • It is a value that can change with time or iterations
      • A constant can be considered something that does not change its data
      • Identifier can be considered a name given to a variable, constant, subroutine or data structure.
      • He won’t ask for definitions in exams
    • We use indentation in pseudocode based on what is a sub part of something
    • Declaration of variatble:
      • Always use small letters for variables
      • When you declare variables, it must be with either = to sign or a reverse arrow.
      • I personally prefer equal to sign
      • Declaration is the initial or original value of the variable
      • For example a=0 means that initially, a has a value of zero.
      • Remember, in the name of the variable, we don’t use spaces. The better way is to start with capital letters. For example say StudentName.
    • We need to total at times. It means adding the inputs of numbers.
      • For this, we use total=  total + number
      • Remember, we can use any variable for the totaling. For example, we can say a= a + nunber
      • Similarly, we can use any variable for the number as well
      • For example, we can say a = a +x
      • The main thing is the addition here.
    • Next, we need to count at times.
      • It means with every step, we want to increase the count value by 1.
      • For example, we can say count = count +1
      • Remember, we can use any variable for counting
      • For example a= a+1
      • Just make sure that the variable you use is unique in the pseudocode and not being used to represent anything else.
    • Data Types
      • String contains a mix of texts, characters and numbers.
      • It must always be inside “” otherwise it won’t display
      • Integer
        • Whole numbers only
      • Real, Single, Double
        • Decimal Numbers
      • Boolean
        • Either true or false, yes or no, or any two choices
      • Char
        • One character, number of symbol
        • It must always be either in “” or ”.
    • Arithmetic Operations
      • +: Addition
      • -: Subtraction
      • *: Multiplication
      • /: Division
      • DIVL provides the while number that comes after the first number is divided by second. Ignores the remainder
      • MOD: Ignores the whole number after the division, provides only the remainder.
      • ^: Exponent or power of something.
    • Remember, programs are run in a sequence
      • They are run from top to down, each statement is run after the other step by step.
    • Selection Rules
      • We use = for equal to
      • We use == for equal to as well
      • We use <> for not equal to
      • We use < for less than
      • We use <= less than or equal to
      • We use > for greater to
      • We use >= for greater than equal to
    • Decision making
      • Sometimes, we need to decide something in the statement.
      • We use IF statement for that purpose.
      • Remember, the syntax is IF _____ THEN _____ ELSE____ ENDIF. Don’t miss the ENDIF part it is extremely important part of the syntax
      • Here, we must remember, that after IF we provide the condition, then on the same line we write THEN
      • Remember, for all parts of syntax we use capital letters
      • Then, on the next line we write what has to happen, in an indent.
      • Then, we  write the ELSE part if an ELSE exists.
      • Otherwise, we write ENDIF directly
      • We write ELSE on the next line, then we write what to happen if the IF statement was not true on the next line, and then we write END IF.
    • Nested IFs
      • Sometimes, we need to write multiple IFs because there are multiple decisions involved.
      • Basically, a nested if is an IF inside a IF.
      • For example, if I input a number, and then I first need to decide if it is greater than 100, if it is not greater than hundred than I need to decide if it is less than 10. In such cases, I would use nested IF.
      • Here, we will do as follows
        • IF x>100 THEN
          • a=a+x
          • ELSE IF x< 10 THEN
            • b=b+x
          • END IF
        • END IF
      • Remember, we need as many endifs as the total ifs we have used.
      • We can have many different ifs inside the same statement as well.
    • SELECT CASE
      • Here, if we have a lot of options we need to decide, we can instead use SELECT CASE syntax instead of using a lot of nested IFs
      • For example
      • I need to check if the input country name is Pakistan, India, Bangladesh or any other, and based on this I need to increase the count of p, i, b or o.
      • Therefore, I will use the following syntax.
        • CASE OF x
          • “Pakistan”
            • p=p+1
          • “India”
            • i=i+1
          • “Bangladesh”
            • b=b+1
          • OTHERWISE
            • o=o+1
        • ENDCASE
      • Remember, otherwise is a part of the syntax for all the options not mentioned directly.
    • BOOLEAN OPEARTORS
      • Basically, it comes under the logic gates section
        • AND
          • Both conditions are true then the result is true
          • Even if one of the two conditions or both conditions false, the answer is false.
        • OR
          • Even if one of the conditions or both conditions true, then it will give true
          • If both conditions false, it will give false.
        • NOT
          • It will reverse the condition
            • If input true, then output false
            • If input false then output true
    • Iteration
      • It means when the same activity has to be repeated constantly for a set number of times.
      • It has three different types, we also call them different types of loops
        • First, we use count-controlled iteration or what we call as the FOR TO NEXT Loop
        • Remember, the FOR loop is used where we have an exact number of iterations to perform. For example, 30 times, 50 times etc.
        • The syntax is as follows:
          • FOR x = 1 TO 50
            • Write the code part that we need to repeat
          • NEXT x
        • For example, if we need to take 30 inputs and then total all of them
        • Therefore
          • FOR x= 1 TO 30
            • Input number
            • a=a+number
          • NEXT x
        • It will take 30 inputs and then the loop will stop
      • A second form of loop is called the pre-condition loop where the condition is checked at the start of the loop
      • If the condition is not satisfied, the loop will never even run once. This is one amazing quality of the WHILE loop
      • The structure is as follows
        • WHILE condition DO
          • Code that has to be repeated
        • ENDWHILE
      • For example, if we want a program that will output the first 10 numbers one by one, the following can be performed
        • x=1
        • WHILE x<11 DO
          • OUTPUT(x)
          • x=x+1
        • ENDWHILE
      • Here, once the number reaches more than 10, or becomes 11, the loop will stop
      • Notice how we used the initial value 1
        • Here, we must always think about the logic being applied
        • Remember, the pseudocode system is flexible to help create the logic we want.
        • Just ensure that the right logic is being applied
    • Post condition Loop
      • A loop where the condition is checked at the end. It means that the loop will run at least once.
      • Here, the REPEAT UNTIL syntax is used
      • REPEAT
        • The code that is to be repeated
      • UNTIL Condition
    • We can convert the loops between each other as well with changes in the syntax.
    • Some other commands are as follows
      • Length of a written string
        • We use LENGTH (“string”)
        • It will return the number of characters.
        • Remember, space is counted as a character as well.
      • SUBSTRING (String, start character, number of characters)
      • Here, the string is the actual sentence etc.
      • The start character is the letter, starting the count from the left side, from where the new string will be generated
      • The number of characters is the number of letters to be extracted.
      • For example SUBSTRING (“I am Hunain”, 6, 4) will return “Huna”, as the fifth character, counting the spaces is H, and the 4 characters including it are Huna.
    • Upper and Lower case
      • UPPER (string) will convert the complete string to upper case letters
      • LOWER (string) will convert the entire string to lower case letters
    • Subroutine
      • A complete self-contained code that has its own identifier.
      • The benefit is that we write such a code once, and then we can just use its identifier to reference wherever it will be used directly without writing it again.
      • Two types
        • Procedures
          • It does not return a value, just runs the code
          • PROCEDURE identifier ()
            • Code to run
          • ENDPROCEDURE
        • For example,
        • PROECDURE Add5Inputs()
          • FOR Count = 1 TO 5
            • Input Number
            • a=a+number
          • NEXT Count
        • ENDPROCEDURE
        • Now, wherever I need to perform the same action again, I will just write Add5Inputs() and it will do the entire code written above inside the procedure
      • A function does a different jo, it will return an answer based on the input we provide
        • FUNCTION identifier()
          • Code that we perform
          • RETURN value
        • ENDFUNCTION
      • For example a function that will first ask the user to enter two values, then add them together and then return the value that is the total will be as follows
        • FUNCTION Add()
          • OUTPUT (“Enter a number”)
          • Input Num1
          • OUTPUT (“Enter another number”)
          • Input Num2
          • Return Num1+Num2
        • ENDFUNCTION
      • Now, the function will provide the totaled value.
    • Scope
      • An area of the program where it can be accessed
      • Global is what can be used by any part of the program
      • Local variable is one that can be used inside a specific area of the program
      • Not tested in our exams.
    • Parameters
      •  A value that a main program sends to the subroutine
      • It is declared within the brackets of the subroutine
      • Rarely tested in exams
  • Library Routines
    • ROUND limits the number of decimal places to a certain extent
    • For example, ROUND (Number, the number of decimal places)
    • For example ROUND (5.1512512, 2) will give 5.15
  • RANDOM
    • It generates a random number between 2 values
    • RANDOM(1,100).
  • Arrays
    • An array is a data structure where we can store multiple pieces of information in the same structure.
    • For example, storing 30 values separately.
    • 1-dimensional array has one row of data
    • Each space on the array is called an index
    • Arrays can have 0 or 1 as the first space, in pseudocode it is usually decided in advance.
    • If I want to store the number 25 in the first location of the array, I can write
    • NumberStore(0)= 25
    • We can also output the data as well or take it out as per requirement.
    • We can put it in a loop as well
    • FOR i = 1 TO 10
      • OUTPUT (Colors(i))
    • NEXT i
    • Here, the 10 outputs will be displayed from the items stored in the array one by one.
  • 2-dimensional arrays
    • Two indices are used, for example Color(0,0)
  • Reading from a file rarely tested in exams
  • Writing on a file is also rarely tested.
Hunain Zia

Hunain Zia has previously achieved considerable success in the high-school educational stream, gaining a massive 154 Total A Grades and 7 Major Distinctions, a process in which he broke/ set 11 different world records, including the most A grades ever achieved, most subjects ever appeared in, most distinctions, gaining distinctions across two separate boards (Pearson Edexcel and CAIE) within the same year/ ever, and even 19 hours of constant examination. All records stand intact today. Hunain pursued his Honors Accounting Degree from the prestigious Bentley University, and then completed an LLB (in Honors) from University of London. Currently, he manages multiple social and commercial projects, has founded digital streams and works tirelessly in the education sector.

Educate A Change focuses on truly bringing change in the educational sector worldwide. All our courses are designed to ensure success, and provide complete preparation without requiring any other external material. Therefore, it takes away the expense of academies, books, past paper compilations and other miscellaneous items. Instead, by just the courses we offer, the student can prepare fully for the best grades in their CAIEs, Edexcel and other high-school exams. The earnings from our course-sales are invested in social projects and growing the free educational activities of Educate A Change.