Here are ten little programs of ten lines or less to introduce new programmers to IDL. This post[^1] is motivated by this [comp.lang.python thread] which became this [page][Simple Python programs] on the Python wiki.

[comp.lang.python thread]: http://groups.google.com/group/comp.lang.python/browse_frm/thread/3eb8837f6dc278c1 "ten small Python programs"
[Simple Python programs]: http://wiki.python.org/moin/SimplePrograms "Simple Python programs"

[^1]: I'm not sure why, but I've had a draft of this post around for almost seven years.

1 line: output, calling a procedure:

print, 'Hello, world!'

2 lines: assignment, calling a function, system variables, array operations, keywords:

x = findgen(360) * !dtor
plot, x, sin(x), xstyle=9, ystyle=8

3 lines: input, output format codes:

name = ''
read, 'What is your name? ', name
print, name, format='("Hello, ", A, "!")'

5 lines: filename handling, reading images, variable metadata, boolean keywords, displaying image:

filename = filepath('people.jpg', subdir=['examples', 'data'])
im = read_image(filename)
dim = size(im, /dimensions)
window, xsize=dim[1], ysize=dim[2], /free, title=file_basename(filename)
tv, im, true=1

6 lines: logical unit numbers, read binary data, contour plots, line continuation:

convec = bytarr(248, 248)
openr, lun, file_which('convec.dat'), /get_lun
readu, lun, convec
free_lun, lun
window, xsize=500, ysize=500, /free
contour, convec, xstyle=1, ystyle=1, $
levels=(max(convec) - min(convec)) * findgen(10) / 9. + min(convec)

7 lines (contributed by Mark Piper): query image, image processing, automatic positioning of images:

file = file_which('moon_landing.png')
!null = query_image(file, info)
astronaut = read_image(file)
window, /free, xsize=3 * info.dimensions[0], ysize=info.dimensions[1]
tv, astronaut, 0
tvscl, sobel(astronaut), 1
tvscl, canny(astronaut), 2

8 lines: writing a function, `compile_opt` statement, `if` statements, `for` loops:

.compile
function mg_fibonacci, x
compile_opt strictarr
if (x eq 0) then return, 0
if (x eq 1) then return, 1
return, mg_fibonacci(x - 1) + mg_fibonacci(x - 2)
end
for i = 0L, 20L do print, i, mg_fibonacci(i)

9 lines (contributed by Mark Piper): array generation, FFTs, line plots, multiple plots/window, query for screen size:

x = (2.0 * !pi) * findgen(100) / 100
y = sin(3.0 * x) + cos(12.0 * x) + cos(25.2 * x)
magspec_y = abs(fft(y))
ss = get_screen_size()
window, /free, xsize=0.4 * ss[0], ysize=0.25 * ss[1]
!p.multi = [0,2,1]
plot, x, y, xtitle='sample number', ytitle='value', title='Series', xstyle=1
plot, magspec_y, xtitle='mode', ytitle='spectral density', $
title='Magnitude Spectrum', xrange=[0, n_elements(x) / 2], xstyle=1
!p.multi = 0

10 lines: maps, read ASCII file, indexed color, structures:

header = strarr(5)
data = replicate({loc:fltarr(2), elev:0, temp:0, dew:0, wspd:0, wdir:0}, 15)
openr, lun, file_which('ascii.txt'), /get_lun
readf, lun, header
readf, lun, data
free_lun, lun
device, decomposed=0
loadct, 5
map_set, limit=[min(data.loc[1, *], max=maxlat), $
min(data.loc[0, *], max=maxlon), maxlat, maxlon], /mercator, /usa
plots, data.loc[0, *], data.loc[1, *], psym=4, color=bytscl(data.temp), $
symsize=2., thick=2