B2.3 Programming constructs: notes and practice

What you need to know

Our summary of the topic in our own words, not the IB guide.

• Write a program whose statements run in the correct order to meet a stated objective
• Write conditional statements using if, else if and else
• Write nested and compound conditions correctly
• Trace a program with branching and state which branch runs for given inputs
• Write a count-controlled loop
• Write a condition-controlled loop and avoid an infinite loop
• Write nested loops, for example to process a two-dimensional structure
• Trace a loop and state the number of iterations and the final values
• Define a function with parameters and a return value, and call it
• Explain the difference between a parameter and an argument, and between returning and printing
• Decompose a long program into functions and explain the benefit of modularisation

Learn it

• Print one line

  Lesson with 2 exercises

• Statements run top to bottom

  Lesson with 2 exercises

• Read a line and print it back

  Lesson with 2 exercises

• Read several lines, use them in any order

  Lesson with 2 exercises

• Capstone: several inputs, several results

  Lesson with 1 exercise

• if

  Lesson with 3 exercises

• else

  Lesson with 3 exercises

• else-if chains; the first true branch wins

  Lesson with 3 exercises

• Comparing text

  Lesson with 2 exercises

• and, or, not

  Lesson with 3 exercises

• Nested conditions

  Lesson with 1 exercise

• Trace a branching program

  Lesson with 2 exercises

• Capstone: several rules decide one answer

  Lesson with 1 exercise

• Loop until a stop value

  Lesson with 3 exercises

• Every loop needs an update; find the infinite loop

  Lesson with 2 exercises

• The counting pattern

  Lesson with 2 exercises

• Sum and average, with an empty-input guard

  Lesson with 3 exercises

• Count-controlled loop

  Lesson with 3 exercises

• Loop bounds from input; a running total over a range

  Lesson with 2 exercises

• Nested loops

  Lesson with 3 exercises

• Trace a loop: iterations and final values

  Lesson with 3 exercises

• Capstone: read a stream, report several statistics

  Lesson with 1 exercise

• Define and call a function

  Lesson with 2 exercises

• Pass a value in

  Lesson with 2 exercises

• Return a value

  Lesson with 3 exercises

• Parameter versus argument; returning versus printing

  Lesson with 4 exercises

• Several parameters; order matters

  Lesson with 2 exercises

• Functions that call your functions

  Lesson with 3 exercises

• Capstone: split a long program into functions

  Lesson with 1 exercise

• Loop over the characters

  Lesson with 5 exercises

Practice questions

Original questions written for the 2027 course, marked as you go. Easiest first.

• Cafe menuCoding · Warm-up
• Count until stopCoding · Warm-up
• Door messagesCoding · Warm-up
• Double a numberCoding · Warm-up
• Even or oddCoding · Warm-up
• First lineCoding · Warm-up
• Floor signCoding · Warm-up
• For vs whileWritten · Warm-up
• Function purposeWritten · Warm-up
• Greeting with a borderCoding · Warm-up
• ID cardCoding · Warm-up
• Is evenCoding · Warm-up
• Loop update ruleWritten · Warm-up
• Message boardCoding · Warm-up
• Old enoughCoding · Warm-up
• Param vs argWritten · Warm-up
• Password checkCoding · Warm-up
• Print starsCoding · Warm-up
• Range with andCoding · Warm-up
• Repeat a characterCoding · Warm-up
• Repeat messageCoding · Warm-up
• Show N timesCoding · Warm-up
• Star bannerCoding · Warm-up
• Swap linesCoding · Warm-up
• Trace: if ageTrace table · Warm-up
• Trace: if elseTrace table · Warm-up
• Absolute valueCoding · Core
• Average scoreCoding · Core
• Check temperatureCoding · Core
• Clamp a valueCoding · Core
• Command checkCoding · Core
• Custom borderCoding · Core
• Count the digitsCoding · Core
• Find infinite loopWritten · Core
• Grade letterCoding · Core
• Grid coordinatesCoding · Core
• Halving stepsCoding · Core
• Integer powerCoding · Core
• Lift distanceCoding · Core
• Largest of threeCoding · Core
• Login checkCoding · Core
• Pass markCoding · Core
• Range checkCoding · Core
• Sign checkCoding · Core
• Star rectangleCoding · Core
• Sum of digitsCoding · Core
• Sum a rangeCoding · Core
• Sum until zeroCoding · Core
• Ticket priceCoding · Core
• Times table rowCoding · Core
• Trace: and orTrace table · Core
• Trace: digit sumTrace table · Core
• Trace: elifTrace table · Core
• Trace: elif updateTrace table · Core
• Trace: gradesTrace table · Core
• Trace: nested gridTrace table · Core
• Trace: return valueTrace table · Core
• Trace: return value (Java)Trace table · Core
• Trace: step loopTrace table · Core
• Trace: sum loopTrace table · Core
• Trace: two ifsTrace table · Core
• Trace: while countdownTrace table · Core
• Weekend checkCoding · Core
• Why decomposeWritten · Core
• Grade reportCoding · Stretch
• Trace table: counting free cinema seatsTrace table · Stretch
• Pay slipCoding · Stretch
• Score reportCoding · Stretch
• Stream statisticsCoding · Stretch
• Trace: nested countTrace table · Stretch

Exam tips for B2.3

• Check loop boundaries carefully. Off-by-one errors are a very common mistake.
• Know the difference between returning a value and printing it.
• Break long answers into small functions. It is easier to write and to mark.