---
title: "Sniper"
id: 57279
type: "computer_media"
slug: "sniper"
url: "http://localhost/computer_media/sniper/"
markdown_url: "http://localhost/computer_media/sniper.md"
published_at: "2024-10-04T08:01:19+00:00"
modified_at: "2026-03-30T21:18:42+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2024/10/167_Snip.png"
excerpt: "A quick-fire reaction game where a target figure flashes on screen and you must hit the right key before time runs out — and it only gets faster."
category:
  - name: "Archived Media"
    slug: "archived-media"
    taxonomy: "category"
    url: "http://localhost/category/archived-media/"
post_tag:
  - name: "Downloadable"
    slug: "downloadable"
    taxonomy: "post_tag"
    url: "http://localhost/tag/downloadable/"
  - name: "TS 1000"
    slug: "ts1000"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts1000/"
model:
  - name: "Timex/Sinclair 1000"
    slug: "ts-1000"
    taxonomy: "model"
    url: "http://localhost/model/ts-1000/"
genre:
  - name: "Game"
    slug: "game"
    taxonomy: "genre"
    url: "http://localhost/type/game/"
media_contents:
  - id: 56734
    title: "Timex Sinclair Public Domain Library Tape 1003"
    type: "computer_media"
    url: "http://localhost/computer_media/timex-sinclair-public-domain-library-tape-1003/"
media_type: "Program"
mediadate: "198x"
images:
  - url: "http://localhost/wp-content/uploads/2024/10/167_Snip.png"
media_type_tags: "Game"
---

Sniper is a reaction-based shooting game where a figure appears at a random horizontal position on screen and the player must press the correct number key before it disappears. The figure is drawn using block graphics and inverse-video characters across four rows, giving it a simple but recognizable silhouette. The target position variable X is multiplied by 3 to space figures across the screen in columns, while T is computed as (X/3 + 1) × SGN(9 − X/3) to map each position to a unique digit key the player must press. The window of opportunity shrinks as the counter C increases, since PAUSE 90−C gives progressively less time to react. POKE 16437,255 is used repeatedly to clear the keyboard buffer before checking INKEY$, preventing stale keypresses from registering as hits.

***

## Program Analysis

### Program Structure

The program is structured as a single main loop running from line 70 to line 300. Initialization (score and counter) happens once at lines 50–60, and the game resets when the counter `C` reaches 40 at line 260, which loops back to line 40 to re-initialize everything. The overall flow is:

1. Initialize score `S=0` and counter `C=0` (lines 50–60)
2. Choose a random column position `X` and compute the expected key `T` (lines 70–80)
3. Draw the target figure at column `X*3` (lines 90–130)
4. Pause for a decreasing time window, then test for the correct keypress (lines 140–160)
5. If correct, draw a “hit” figure, update and display score, and pause (lines 170–240)
6. Clear screen, increment counter, pause a random interval, and repeat (lines 250–300)

### Position and Key Mapping

The random column index is generated as `X = INT(RND * 9.9)`, giving values 0–9. This is then scaled to screen columns with `X = X * 3`, spacing figures across 30 columns in steps of 3. The expected key digit `T` is calculated at line 80 as `(X+1) * SGN(9-X)` (using the pre-scaled X). For values 0–8 this yields digits 1–9 since SGN(9−X) = 1; for X=9 it yields 0 since SGN(0)=0. This neatly maps each of the ten positions to a unique digit key 1–9 and 0.

### Difficulty Progression

The reaction window is controlled by `PAUSE 90-C` at line 140, where `C` increments by 1 each round (line 290) and resets to 0 every 40 rounds. This means the display time shrinks from approximately 1.5 seconds at the start of a cycle down to about 0.8 seconds by round 40, creating a gradual difficulty ramp within each 40-round cycle.

### Keyboard Buffer Management

`POKE 16437,255` appears at lines 150, 240, and 280. Address 16437 is the LAST K system variable, which holds the last key pressed. Poking it with 255 effectively invalidates the stored keypress, ensuring that `INKEY$` only returns a fresh keypress made during the current window. This prevents a key held down from a previous round from accidentally scoring a hit.

### Graphics Techniques

The target figure spans four PRINT AT rows and uses a combination of block graphics escapes and inverse-video characters. The head is drawn as `" O"`, the body uses inverse-space characters (shown as filled blocks) for a torso, and the legs use block graphic characters. The “hit” animation at lines 170–200 replaces the figure with a different arrangement suggesting a falling or exploding character, providing visual feedback for a successful shot.

| Line | Row offset | Content description |
| --- | --- | --- |
| 100 | Row 4 | Head: space + “O” |
| 110 | Row 5 | Shoulders: block graphics with inverse space (torso) |
| 120 | Row 6 | Body: space + inverse-space + two spaces |
| 130 | Row 7 | Legs: block graphics with inverse space |

### Notable Idioms and Anomalies

- `STR$ T` at line 160 converts the numeric digit T to a string for comparison with `INKEY$`, which always returns a string — a necessary type-matching technique.
- The inter-target pause at line 270, `PAUSE INT(RND*120)+30`, adds 30–149 frames of random delay between figures, preventing the player from anticipating timing.
- The `REM "SNIPER"` at line 10 serves as the program title; lines 40–300 form the actual code, with the gap from 10 to 40 being cosmetic.
- Line 310 (`SAVE "1016%7"`) and line 320 (`LIST`) are utility lines appended after the main program body and are not part of normal execution flow.
- There is no explicit “Game Over” message or final score display when the 40-round cycle completes — the game simply resets silently at line 260.

## Source Code

```
  10 REM "SNIPER"
  40 CLS 
  50 LET S=0
  60 LET C=0
  70 LET X=INT (RND*9.9)
  80 LET T=(X+1)*SGN (9-X)
  90 LET X=X*3
 100 PRINT AT 4,X;" O"
 110 PRINT AT 5,X;"\''% \''"
 120 PRINT AT 6,X;" %  "
 130 PRINT AT 7,X;"\ .% \. "
 140 PAUSE 90-C
 150 POKE 16437,255
 160 IF INKEY$<>STR$ T THEN GOTO 250
 170 PRINT AT 4,X;"\'.O\.'"
 180 PRINT AT 5,X;" %  "
 190 PRINT AT 6,X;" %  "
 200 PRINT AT 7,X;"\.' \'."
 210 LET S=S+1
 220 PRINT AT 15,0;"SCORE";S
 230 PAUSE 60
 240 POKE 16437,255
 250 CLS 
 260 IF C=40 THEN GOTO 40
 270 PAUSE INT (RND*120)+30
 280 POKE 16437,255
 290 LET C=C+1
 300 GOTO 70
 310 SAVE "1016%7"
 320 LIST
```