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Cheatography

Algorithm IGCSE Cheat Sheet by [deleted]

This is a cheat sheet for pseudocode in Computer Science IGCSE ~

Data Types & Structures

INTEGER (whole numbers)
1, 2, 45, 231, -2, -213
REAL (decimal numbers)
1.23, 938.23­2312, -23.233
STRING (words or sentences)
“Hello World”, “123 bipbop”
CHARACTER (one character or alphabet)
‘A’, ‘b’, ‘Y’, ‘o’, ‘1’, ‘8’, ‘d
BOOLEAN (true or false)
TRUE, FALSE, TRUE, TRUE
ARRAY (many words or numbers)
[“Hi”, “me not smart”, 174, 23, “12 bipbop”, -1234]
Rules:
INT and REAL are typed as numbers only
STR must be in double quotation marks i.e. "­Hel­lo"
CHAR must be in single quotation marks i.e. 'H'
BOOL must be in either TRUE or FALSE
Array can be assigned to variables and must be inside braces. i.e. names = ["An­dy", "­Cin­dy", "­Bob­by"]

Operators (Arith­metic)

Operators
Examples
It Will Give
+ (plus)
5 + 5
10
- (minus)
8 - 3
5
* (multiply)
6*2
12
/ (divide)
8/4
2
^ (power)
2^3
8
DIV (dividend)
12 DIV 5
2
MOD (modulo)
10 MOD 5
0
Note: MOD will give you the remainder of the number

Operators (Assig­nment)

Operators
Examples
> (greater than sign)
100 > 5
< (lesser than sign)
60 < 150
<> (not equal sign)
7 <> 25
= (equal sign)
12 = 12
The >= operator means greater than or equal to
The <= operator means lesser than or equal to

Operators (boolean)

Operators
Examples
AND
TRUE AND TRUE = TRUE
OR
TRUE OR FALSE = TRUE
NOT
NOT FALSE = TRUE
Boolean Operators are also called Logical Operators. AND means conjun­ction, OR means disjun­ction, NOT means negation
 

The FOR Loop

FOR LOOP
Use a FOR loop when you know how many times it'll run
    
The syntax:
FOR variable = something to something
    do something
NEXT

The example:
FOR number = 1 to 3:
    PRINT number
NEXT
Running this on raptor/ other engines will output:
1
2
3

REPEAT Loop

THE REPEAT LOOP
Use a REPEAT loop when you know how many times it'll run

The syntax:
REPEAT
    do something
UNTIL something

The example:
number = 1
REPEAT
    PRINT number
    number = number + 1
UNTIL number = 3
Running this on raptor/ other engines will output:
1
2
3

WHILE Loop

THE WHILE LOOP
Use WHILE loop when you don't know how many times it'll run

The syntax:
WHILE something DO
    do something
ENDWHILE

The example:
number = 1
WHILE number < 3 DO
    PRINT number
    number = number + 1
ENDWHILE
If you put this in raptor­/other engines they will output:
1
2
3

Writing An Algorithm Example

You are tasked to find out what is the 16th number in the Fibonacci sequence, how do you do it?
fib_0 = 0
fib_1 = 1
find_num = 16
FOR i = 0 to find_num
___ fib_2 = fib_0 + fib_1
___ fib_0 = fib_1
___ fib_1 = fib_2
PRINT "The 16th number is: ", fib_2
 
Answer of Output = 987
Fibonacci Sequence is a sequence where each number is the sum of the two preceding ones. For example: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34
 

Condit­ional Statements (IF)

Syntax:
IF condition
    THEN do something
    ELSE do something else
ENDIF

Example:
khaisar_height = 100
IF khaisar_height < 120
    THEN PRINT “Please enter the kids room”
    ELSE PRINT “Please enter the teenagers room”
ENDIF
Desc­rip­tion:
Condit­ional Statements are IF statem­ents. The IF statement check if a condition is TRUE or FALSE.

In the English language, we say:
If you come to the party, I'll buy one pizza.

In the computer language. We say it like this:
IF answer = “YES” THEN pizza = 1 ENDIF
As simple as that!

Extended IF statement

IF grade > 90 AND behavior > 80
    THEN PRINT "Excellent"
ELIF grade > 80 AND behavior > 70
    THEN PRINT "Well Done"
ELIF grade > 70 AND behavior > 60
    THEN PRINT "Good Job"
ELSE PRINT "Improvement is needed!"
ENDIF
IF and ELIF (else if) are used for a choice between several different values. You can either use ELIF or CASE, it is up to you.

CASE OF

Syntax:
CASE ... OF
    something
    OTHERWISE something
ENDCASE

Example:
CASE grade OF
    'A' : PRINT "Excellent"
    'B' : PRINT "Well Done"
    'C' : PRINT "Good Job"
    'D' : PRINT "Do Better"
    'F' : PRINT "Find Another Answer"
    OTHERWISE PRINT "Improve next time"
ENDCASE
CASE is another condit­ional statement that is use for several different values

Functions

The syntax:

FUNCTION do_something(Parameters)
    statements
    RETURN something
END PROCEDURE

Example:

FUNCTION count_pizza_slices(number_of_pizza)
    number_of_pizza_slices = 0
    number_of_pizza_slices = number_of_pizza * 8
    RETURN number_of_pizza_slices
END PROCEDURE
Running this on a engine­/idle:
count_­piz­za_­sli­ces(5)

Output:
40

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