From QB64 Wiki
Subs, short for subroutines, are like statements but user-defined. You define a sub by using the statement SUB and when called it will execute the code within the SUB until it reaches END SUB or EXIT SUB.
Subs do not return a value, however; altering the variables that are used as arguments within the sub will cause the same changes to the variables outside the sub. This also applies to user-defined functions. Variables that are not arguments of the sub will not be changed if used within the sub unless they are SHARED.
The subs has to be located after all other code, this also applies to user-defined functions.
Example 1: Demonstration of some subs.
printsometext CALL printmoretext SUB printsometext PRINT "This is within the printsometext sub." EXIT SUB PRINT "This is never shown as it encounters EXIT SUB first." END SUB SUB printmoretext PRINT "This is within the printmoretext sub." END SUB
Example 2: Variables that are used as arguments changes outside the sub when they are changed within the sub.
demo hal, bal 'the variables hal and bal are used as arguments when calling the sub. PRINT hal, bal 'the variables have now been changed by the sub. hal = 0 bal = 0 demo 1, 2 PRINT hal, bal 'the variables have not been changed by the sub as the variables wasn't used as arguments. SUB demo (hal, bal) hal = 3 bal = 4 END SUB