Start with the recap, study the fully worked examples, then use the practice problems to
check your understanding of Pseudocode.
This page combines explanation, solved examples, and follow-up practice so you can move
from recognition to confident problem-solving in CS Thinking.
Concept Recap
An informal, human-readable description of an algorithm using structured language that resembles code but is not tied to any specific programming language. Pseudocode uses plain English mixed with programming constructs like IF, WHILE, and FOR to describe logic without worrying about syntax rules.
Pseudocode is a rough draft for code — write the logic in plain English first, then translate to real code.
Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.
What to Focus On
Core idea:Pseudocode lets you focus on logic without worrying about syntax. It's a planning tool, not a running program.
Common stuck point:There's no single 'correct' pseudocode format. It just needs to be clear and unambiguous to the reader.
Sense of Study hint:When writing pseudocode, use indentation to show structure (loops, conditionals), use uppercase for keywords (IF, WHILE, FOR, PRINT), and write one action per line. Focus on the logic, not the syntax—if a human can read it and understand the steps, it is good pseudocode.
Common Mistakes to Watch For
Before you work through the examples, skim the mistake guide so you know which shortcuts and
sign errors to avoid.
Write pseudocode for a program that asks the user for two numbers and outputs the larger one.
Answer
INPUT a, b. IF a > b THEN OUTPUT a ELSE OUTPUT b. Pseudocode describes logic without language-specific syntax.
First step
1
Step 1: Get the inputs: a = INPUT('Enter first number'). b = INPUT('Enter second number').
Full solution
2
Step 2: Compare: IF a > b THEN OUTPUT a. ELSE OUTPUT b.
3
Step 3: Pseudocode does not follow the syntax of any specific language — it uses plain English-like statements to describe the logic clearly.
Pseudocode is an informal way of describing an algorithm using structured English. It focuses on logic rather than syntax, making it accessible to anyone regardless of programming language knowledge.
Example 2
medium
Convert the following Python code to pseudocode: total = 0; for i in range(1, 11): if i % 2 == 0: total += i; print(total).
Example 3
easy
Write pseudocode to read three numbers and output their sum.
Example 4
medium
Write pseudocode for: read a number n, output 'positive' if n>0, 'negative' if n<0, else 'zero'.
Example 5
medium
Write pseudocode that asks for a password until the user enters 'secret'.WHILE password incorrect: keep asking
Example 6
hard
Trace a swap: SET a TO 7; SET b TO 2; SET t TO a; SET a TO b; SET b TO t. What are a and b?
Example 7
hard
Trace: SET arr TO [3,1,4,1,5,9,2,6]; bubble-sort one pass swapping adjacent if out of order. Show arr after one pass.
Example 8
challenge
Trace Euclid's algorithm: SET a TO 48; SET b TO 18; WHILE b != 0: SET t TO b; SET b TO a MOD b; SET a TO t. What is a at the end?
Practice Problems
Try these problems on your own first, then open the solution to compare your method.
Example 1
medium
Write pseudocode for a program that reads a list of 10 numbers and outputs how many are above average.
Example 2
hard
A colleague writes pseudocode that mixes Python syntax, uses unclear variable names, and skips steps. Identify three problems with: 'x = input(); for y in x: if y == z: cnt+=1; print(cnt)'. Rewrite it properly.
Example 3
easy
Trace this pseudocode: SET x TO 5; SET y TO 3; SET z TO x + y; OUTPUT z. What is printed?trace: what value does OUTPUT z print?
Example 4
easy
In pseudocode, which keyword introduces a two-way decision?
Example 5
easy
Trace: SET total TO 0; FOR i FROM 1 TO 3: SET total TO total + i. What is total at the end?FOR i FROM 1 TO 3 accumulating total
Example 6
easy
Which is the BEST pseudocode line, given the rule 'avoid language-specific syntax'? (a) int x = 5; (b) SET x TO 5
Example 7
easy
Trace: SET a TO 4; IF a > 2 THEN OUTPUT "big" ELSE OUTPUT "small". What is printed?IF a > 2 THEN big ELSE small
Example 8
easy
What is the main PURPOSE of writing pseudocode before real code?
Example 9
easy
Trace: SET n TO 10; SET n TO n - 4; SET n TO n * 2; OUTPUT n. What is printed?
Example 10
easy
Which control structure repeats steps WHILE a condition stays true?
Example 11
medium
Trace: SET s TO 0; FOR i FROM 1 TO 4: IF i is even THEN SET s TO s + i. What is s?
Example 12
medium
Trace: SET x TO 2; WHILE x < 20: SET x TO x * 3. What is x when the loop ends?WHILE x < 20: x = x * 3
Example 13
medium
Translate to pseudocode intent: a program reads two numbers and prints the larger. Which condition is correct?
Example 14
medium
Trace: SET count TO 0; FOR each c IN "abca": IF c = "a" THEN SET count TO count + 1. What is count?
Example 15
medium
Trace nested logic: SET r TO 0; FOR i FROM 1 TO 2: FOR j FROM 1 TO 2: SET r TO r + 1. What is r?
Example 16
medium
Trace: SET x TO 7; IF x > 10 THEN OUTPUT "A" ELSE IF x > 5 THEN OUTPUT "B" ELSE OUTPUT "C". Printed?nested IF-ELSE IF: x=7, which branch runs?
Example 17
medium
A spec says: 'repeat asking for a password until it is correct'. Which loop fits best?
Example 18
medium
Trace: SET p TO 1; FOR i FROM 1 TO 4: SET p TO p * i. What is p (this computes a factorial)?factorial loop: FOR i FROM 1 TO 4, p = p * i
Example 19
medium
Trace: SET x TO 16; SET steps TO 0; WHILE x > 1: SET x TO x div 2; SET steps TO steps + 1. What is steps?
Example 20
challenge
Trace this swap: SET a TO 3; SET b TO 8; SET t TO a; SET a TO b; SET b TO t. What are a and b at the end?three-step swap using a temp variable t
Example 21
challenge
Trace: SET n TO 13; SET out TO ""; WHILE n > 0: SET out TO (n mod 2) JOINED-BEFORE out; SET n TO n div 2. What is out?
Example 22
challenge
Two pseudocode versions sum 1..n. Version X uses a FOR loop adding each i. Version Y outputs n*(n+1)/2. For n=100, do they agree, and on what value?
Example 23
easy
Trace: SET a TO 3; SET b TO 4; SET c TO a * b; OUTPUT c. What is printed?
Example 24
easy
Trace: SET s TO 0; FOR i FROM 1 TO 5: SET s TO s + i. What is s?
Example 25
easy
Which keyword introduces a loop that repeats a fixed number of times in pseudocode: WHILE or FOR?
Example 26
easy
Trace: SET x TO 10; IF x >= 10 THEN OUTPUT 'yes' ELSE OUTPUT 'no'. What is printed?IF x >= 10 THEN yes ELSE no
Example 27
easy
Trace: SET n TO 5; SET n TO n + 3; SET n TO n * 2. What is n at the end?
Example 28
medium
Trace: SET total TO 0; FOR i FROM 1 TO 6: IF i MOD 2 = 1 THEN SET total TO total + i. What is total?
Example 29
medium
Trace: SET x TO 1; WHILE x < 50: SET x TO x * 2. What is x when the loop ends?WHILE x < 50: x = x * 2
Example 30
medium
Trace nested loops: SET r TO 0; FOR i FROM 1 TO 3: FOR j FROM 1 TO 3: SET r TO r + 1. What is r?
Example 31
medium
Trace: SET p TO 1; FOR i FROM 1 TO 5: SET p TO p * i. What is p (a factorial)?
Example 32
medium
Trace: SET count TO 0; FOR each c IN "hello": IF c = 'l' THEN SET count TO count + 1. What is count?
Example 33
medium
Trace: SET x TO 20; SET steps TO 0; WHILE x > 1: SET x TO x div 2; SET steps TO steps + 1. What is steps?
Example 34
medium
Trace: SET arr TO [4, 7, 2, 9, 5]; SET m TO arr[0]; FOR i FROM 1 TO 4: IF arr[i] > m THEN SET m TO arr[i]. What is m?
Example 35
medium
What is wrong with this pseudocode for the rule 'avoid language-specific syntax': `for(int i=0;i<10;i++){total+=i;}`
Example 36
hard
Trace: SET n TO 10; SET out TO ''; WHILE n > 0: SET out TO (n MOD 2) PREPENDED-TO out; SET n TO n DIV 2. What is out?
Example 37
hard
Write pseudocode that outputs how many numbers in a list of 10 are above the average.
Example 38
hard
Trace linear search: SET arr TO [3, 8, 5, 9, 2]; SET target TO 9; FOR i FROM 0 TO 4: IF arr[i] = target THEN OUTPUT i AND STOP. What is output?linear search: find index of target=9 in arr
Example 39
hard
Trace: SET x TO 81; SET steps TO 0; WHILE x > 1: SET x TO x DIV 3; SET steps TO steps + 1. What is steps?
Example 40
challenge
Two pseudocode versions sum 1..n. Version X loops adding each i. Version Y outputs n*(n+1)/2. For n=200, do they agree, and on what value?