# Iteration (Loops)

> Cambridge Assessment International Education (CAIE) Pseudocode Reference Guide
> Applicable Syllabus: **IGCSE & A Level**

Count-controlled FOR..TO..STEP..NEXT, post-condition REPEAT..UNTIL, and pre-condition WHILE..ENDWHILE loops in Cambridge pseudocode.

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Three standard loop constructs: count-controlled (`FOR..NEXT`), post-condition (`REPEAT..UNTIL`), and pre-condition (`WHILE..ENDWHILE`).

### Standard Loop Constructs

```pseudocode
// 1. FOR loop (count-controlled)
FOR i <- 1 TO 10
   OUTPUT "Index: ", i
NEXT i

// FOR with STEP increment (positive or negative)
FOR i <- 10 TO 0 STEP -2
   OUTPUT i
NEXT i

// 2. REPEAT .. UNTIL (post-condition)
// Executes at least once; terminates when condition evaluates to TRUE
REPEAT
   OUTPUT "Please enter the password"
   INPUT Password
UNTIL Password = "Secret"

// 3. WHILE .. ENDWHILE (pre-condition)
// Condition tested before each iteration; may execute zero times
WHILE Number > 9
   Number <- Number - 9
ENDWHILE
```

### Syllabus Distinction: DO Keyword

Some IGCSE (0478) materials include a `DO` keyword after the `WHILE` condition (e.g. `WHILE x < 5 DO`). The AS & A Level (9618) specification omits `DO` — the condition is followed directly by the indented loop body. Both styles are valid and accepted in exams.

### Nested FOR Loop Example (2D Accumulation)

```pseudocode
Total <- 0
FOR Row <- 1 TO MaxRow
   RowTotal <- 0
   FOR Column <- 1 TO 10
      RowTotal <- RowTotal + Amount[Row, Column]
   NEXT Column
   OUTPUT "Total for Row ", Row, " is ", RowTotal
   Total <- Total + RowTotal
NEXT Row
OUTPUT "The grand total is ", Total
```


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