# Procedures & Functions

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

Modular Cambridge pseudocode subroutines: PROCEDURE with CALL, FUNCTION with RETURN, and parameter passing by value (BYVAL) and reference (BYREF).

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Procedures perform actions and are invoked with `CALL`. Functions return a single value via `RETURN` and are called as part of an expression (not with `CALL`). IGCSE uses ordinary typed parameters. Explicit pass-by-value (`BYVAL`, default) and pass-by-reference (`BYREF`) modes are AS & A Level (9618) extensions.

### Procedures (CALL)

```pseudocode
// Without parameters
PROCEDURE DefaultSquare()
   CALL Square(100)
ENDPROCEDURE

// With parameters
PROCEDURE Square(Size : INTEGER)
   FOR Side <- 1 TO 4
      CALL MoveForward(Size)
      CALL Turn(90)
   NEXT Side
ENDPROCEDURE

CALL Square(50)
```

### Functions (RETURN)

```pseudocode
FUNCTION Max(Number1 : INTEGER,
             Number2 : INTEGER)
             RETURNS INTEGER
   IF Number1 > Number2 THEN
      RETURN Number1
   ELSE
      RETURN Number2
   ENDIF
ENDFUNCTION

// Called as part of an expression
OUTPUT "Penalty = ", Max(10, Distance*2)
```

### Passing by Reference (BYREF)

```pseudocode
// BYREF allows the procedure to modify the caller's variables directly
PROCEDURE SWAP(BYREF X : INTEGER, BYREF Y : INTEGER)
   Temp <- X
   X <- Y
   Y <- Temp
ENDPROCEDURE

// Note: If not specified, BYVAL (pass by value) is assumed.
// Parameters should NOT be passed BYREF to a function.
```


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