Question

I am trying to do a simple task of appending a number to a string multiple times, and hoping that this will build a string.

But it is not working, each call to (string-append ....) seems to do nothing at all.

Here is my code:

(define myString "")
(string-append (number->string 4) myString)
(string-append (number->string 5) myString)
(string-append (number->string 6) myString)
(string-append (number->string 7) myString)
(display myString)

this displays:

“4”

“5”

“6”

“7”

and a blank line for (display myString)

What am I doing wrong?

also if I do it the other way like so it doesn’t work either:

(define myString "")
(string-append myString (number->string 4))
(string-append myString (number->string 5))
(string-append myString (number->string 6))
(string-append myString (number->string 7))
(display myString)

Thanks for any help

Answer 1

string-append does not alter an existing string; it returns a new string that is the result of the operation.

If this seems unusual, consider the addition operator, +. When I write

3+4

I’m not changing 3 into 7, just returning the result of the operation.

So, in your case, if you write

(define my-string (string-append (number->string 4) (number->string 5)))
(display my-string)

You should see

45

To advise you further, it might help to know where you’re heading with this.