Learn

FreeBASIC distinguishes:

• Sub — does work, no return value
• Function — returns a value

Sub Greet(name AS STRING)
    PRINT "Hello, " + name
End Sub

Function Square(n AS INTEGER) AS INTEGER
    Return n * n
End Function

Greet("Ada")
PRINT Square(5)

Functions return via Return (modern) or by assigning to the function name (classic):

Function Cube(n AS INTEGER) AS INTEGER
    Cube = n * n * n        ' classic style
End Function

Pass-by-reference with BYREF:

Sub Swap(BYREF a AS INTEGER, BYREF b AS INTEGER)
    DIM tmp AS INTEGER
    tmp = a
    a = b
    b = tmp
End Sub

Default is BYVAL (by value) - a Sub that assigns to a plain n AS INTEGER parameter changes only its own copy. BYREF is what makes a parameter an output parameter.

Default arguments:

Function Greet(name AS STRING, greeting AS STRING = "Hello") AS STRING
    Return greeting + ", " + name
End Function

PRINT Greet("Ada")              ' Hello, Ada
PRINT Greet("Ada", "Hi")        ' Hi, Ada

Recursion works fine — no special keyword needed.

Printing a number without the space in front of it

PRINT reserves one column for a number's sign, so a positive number comes out with a leading space. The grader compares that space, and it is the difference between passing and failing this lesson's exercise:

PRINT 1024              ' writes " 1024" - note the space
PRINT LTRIM(STR(1024))  ' writes "1024"
PRINT "n=" & 1024       ' writes "n=1024" - & converts without padding

STR converts a number to a string, LTRIM strips the leading blank, and & concatenates a number onto a string without adding anything.