---
title: "Addition Through 7 Digits"
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published_at: "2026-11-11T08:03:14+00:00"
modified_at: "2026-11-11T08:03:14+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2026/11/addition-through-7-digits-1.png"
excerpt: "Add up numbers of up to seven digits on the ZX80, getting around its 16-bit integers by keeping each digit in an array."
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  - name: "Francis LeBaron"
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download_url: "https://archive.org/download/timex-sinclair-software-archive/Addition%20Through%207%20Digits%20%281981%29%28LeBaron%2C%20Francis%29%28ZX80%29%28US%29%28Program%29.zip"
mediadate: "1981"
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    title: "Syns of Omission"
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---

# Addition Through 7 Digits

The 4K ZX80 handles whole numbers only up to 32767. This program keeps a running total of seven digits, one digit per array element, and does the carrying itself. Enter a number of up to seven digits and press NEWLINE; enter another and the running total appears. As printed, zeros show only as spaces, and a carry is not added correctly.

In the March 1981 issue the author added line 225 LET FL=1, which prints zeros inside numbers, and corrected line 140 to LET Y(I+1)=Y(I+1)+1. The download has both versions. The printed Syntactic Sum of the original, 28812, lost its minus sign: the listing sums to -28812. Line 150 jumps to line 95, which does not exist.

Published in Syntax February 1981 ([Addition Through 7 Digits](https://timexsinclair.com/article/addition-through-7-digits/)).

## Source Code

```
  5 DIM X(7)
  7 DIM Y(7)
 10 INPUT A$
 20 FOR N=1 TO 7
 30 LET X(N)=CODE(A$)-28
 35 IF X(N)<0 THEN GO TO 70
 37 IF X(N)>9 THEN STOP
 50 LET A$=TL$(A$)
 60 NEXT N
 70 LET M=N-1
 80 FOR I=1 TO N-1
 90 LET Y(I)=Y(I)+X(M)
 97 IF Y(I)>9 THEN GO TO 130
100 LET M=M-1
110 NEXT I
120 GO TO 200
130 LET Y(I)=Y(I)-10
140 LET Y(I+1)=Y(I)+1
150 GO TO 95
200 LET M=7
202 LET FL=0
210 FOR I=1 TO 7
212 IF FL>0 THEN GO TO 220
214 IF Y(M)=0 THEN GO TO 260
215 LET FL=0
220 PRINT Y(M);
230 LET M=M-1
240 NEXT I
245 PRINT
250 GO TO 10
260 PRINT " ";
270 GO TO 230
```