Sum of multiples of powers of ten of an integer

Question

Write a function to produce, for a non-negative integer, a string containing a sum of terms according to the following:

3 -> "3"

805 -> "800 + 5"

700390 -> "700000 + 300 + 90"

0 -> "0"

13 -> "10 + 3"

200 -> "200"

Any input other than a non-negative integer can be ignored. Zero terms must be skipped unless the input is 0. Terms must go from largest to smallest. The plus signs must have only a single space on either side.

This is code golf; fewest number of bytes wins.

Answer 1

Jelly, 14 bytes

DḊƬḌINḟ0ȯ0j”+K

A full program which prints the result

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How?

DḊƬḌINḟ0ȯ0j”+K - Main Link: integer, n       e.g. 805
D              - to base ten                      [8,0,5]
  Ƭ            - collect until a fixed point:
 Ḋ             -   dequeue                        [[8,0,5],[0,5],[5],[]]
   Ḍ           - from base ten (vectorises)       [ 805,    5,    5,  0]
    I          - incremental differences          [    -800,   0,   -5 ]
     N         - negate                           [     800,   0,    5 ]
      ḟ0       - filter discard zeros             [     800,         5 ]
        ȯ0     - OR zero (replacing an empty list with 0)
          j”+  - join with '+' characters         [     800,  '+',   5 ]
             K - join with space characters       [800,' ','+',' ',5]
               - implicit, smashing print         "800 + 5"

Answer 2

APL (Dyalog Unicode), 31 bytes^SBCS

Anonymous tacit prefix function, taking the number as a string.

(1↓∘∊1@1∘×⊆⌽∘⍳∘≢('+',10⊥↑)¨⊢)⍎¨

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⍎¨ execute each character (this gives the digits as numbers)

(…) apply the following anonymous tacit prefix function to that:

 …(…)¨⊢ apply the below function between each element and the corresponding element of…

 ⌽ the reversal
 ∘ of
 ⍳ the ɩndices (1…N)
 ∘ of
 ≢ the tally of digits

  ↑ take that many elements, padding with zeros (as there's only ever one)

  10⊥ evaluate that in base ten

  '+', prepend a plus

 …⊆ partition it beginning a new segment where indicated by:

 1@1 a one at the first element
 ∘ of
 × the sign (0 for 0; 1 for all other)

1↓ drop the first
∘ of
∊ the ϵnlisted (flattened) data

Answer 3

Perl 5 -p, 53 bytes

$&&&push@a,$&.y//0/cr while s/.//;$"=" + ";$_="@a"||0

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