Changing string variable value within Sub

[RhoSigma]

When I run the following program:

Code: (Select All)

a$ = "Hello"

Print "a$ as assigned="; a$

abc a$

Print "a$ AFTER sub="; a$



Print



a$ = "Hello"

Print "a$ as assigned="; a$

abc a$ + " col=10 row=10 height=1 len=50"

Print "a$ AFTER sub="; a$







Sub abc (g$)

    Print "value within the sub="; g$

    g$ = g$ + " world"

End Sub

I get the following output:

a$ as assigned=Hello
value within the sub=Hello
a$ AFTER sub=Hello world

a$ as assigned=Hello
value within the sub=Hello col=10 row=10 height=1 len=50
a$ AFTER sub=Hello


The first instance works as expected - I assign a$, pass it to the sub, alter the value, and upon return it has retained the changed from the Sub.

BUT...why is it that when I pass a$ with a static string, I get all of that value passed to the Sub (Hello col=10 row=10 height=1 len=5), but I cannot retain any changes when we return from the Sub ?  Regardless of what I change g$ to in the sub it always reverts back to Hello.

... because line 10 of your code creates a temporary string build from the current a$ contents and the literal string you add to it, that temporary string is then passed to the sub and not the original a$, i.e. the sub only modifies the temporary string it got passed, but that is discarded as soon as the sub returns and a$ is in fact never touched by the sub.